Channel access method for performing transmission in unlicensed band, and device using same

ABSTRACT

A base station of a wireless communication system is disclosed. The base station of wireless communication includes a communication module and a processor. The processor is configured to receive a grant for scheduling a plurality of uplink transmissions from the base station, and when the UE attempts to a first fixed duration-based channel access for a first transmission which is one of the plurality of uplink transmission and fails in the first fixed duration-based channel access, attempt to a second fixed duration-based channel access for a second transmission which is a transmission following the first transmission.

TECHNICAL FIELD

The present invention relates to a wireless communication system.Specifically, the present invention relates to a channel access methodand a device using the same in a wireless communication system operatingin an unlicensed band.

BACKGROUND ART

After commercialization of 4th generation (4G) communication system, inorder to meet the increasing demand for wireless data traffic, effortsare being made to develop new 5th generation (5G) communication systems.The 5G communication system is called as a beyond 4G networkcommunication system, a post LTE system, or a new radio (NR) system. Inorder to achieve a high data transfer rate, 5G communication systemsinclude systems operated using the millimeter wave (mmWave) band of 6GHz or more, and include a communication system operated using afrequency band of 6 GHz or less in terms of ensuring coverage so thatimplementations in base stations and terminals are under consideration.

A 3rd generation partnership project (3GPP) NR system enhances spectralefficiency of a network and enables a communication provider to providemore data and voice services over a given bandwidth. Accordingly, the3GPP NR system is designed to meet the demands for high-speed data andmedia transmission in addition to supports for large volumes of voice.The advantages of the NR system are to have a higher throughput and alower latency in an identical platform, support for frequency divisionduplex (FDD) and time division duplex (TDD), and a low operation costwith an enhanced end-user environment and a simple architecture.

For more efficient data processing, dynamic TDD of the NR system may usea method for varying the number of orthogonal frequency divisionmultiplexing (OFDM) symbols that may be used in an uplink and downlinkaccording to data traffic directions of cell users. For example, whenthe downlink traffic of the cell is larger than the uplink traffic, thebase station may allocate a plurality of downlink OFDM symbols to a slot(or subframe). Information about the slot configuration should betransmitted to the terminals.

In order to alleviate the path loss of radio waves and increase thetransmission distance of radio waves in the mmWave band, in 5Gcommunication systems, beamforming, massive multiple input/output(massive MIMO), full dimensional MIMO (FD-MIMO), array antenna, analogbeam-forming, hybrid beamforming that combines analog beamforming anddigital beamforming, and large scale antenna technologies are discussed.In addition, for network improvement of the system, in the 5Gcommunication system, technology developments related to evolved smallcells, advanced small cells, cloud radio access network (cloud RAN),ultra-dense network, device to device communication (D2D), vehicle toeverything communication (V2X), wireless backhaul, non-terrestrialnetwork communication (NTN), moving network, cooperative communication,coordinated multi-points (CoMP), interference cancellation, and the likeare being made. In addition, in the 5G system, hybrid FSK and QAMmodulation (FQAM) and sliding window superposition coding (SWSC), whichare advanced coding modulation (ACM) schemes, and filter bankmulti-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparsecode multiple access (SCMA), which are advanced connectivitytechnologies, are being developed.

Meanwhile, in a human-centric connection network where humans generateand consume information, the Internet has evolved into the Internet ofThings (IoT) network, which exchanges information among distributedcomponents such as objects. Internet of Everything (IoE) technology,which combines IoT technology with big data processing technologythrough connection with cloud servers, is also emerging. In order toimplement IoT, technology elements such as sensing technology,wired/wireless communication and network infrastructure, serviceinterface technology, and security technology are required, so that inrecent years, technologies such as sensor network, machine to machine(M2M), and machine type communication (MTC) have been studied forconnection between objects. In the IoT environment, an intelligentinternet technology (IT) service that collects and analyzes datagenerated from connected objects to create new value in human life canbe provided. Through the fusion and mixture of existing informationtechnology (IT) and various industries, IoT can be applied to fieldssuch as smart home, smart building, smart city, smart car or connectedcar, smart grid, healthcare, smart home appliance, and advanced medicalservice.

Accordingly, various attempts have been made to apply the 5Gcommunication system to the IoT network. For example, technologies suchas a sensor network, a machine to machine (M2M), and a machine typecommunication (MTC) are implemented by techniques such as beamforming,MIMO, and array antennas. The application of the cloud RAN as the bigdata processing technology described above is an example of the fusionof 5G technology and IoT technology. Generally, a mobile communicationsystem has been developed to provide voice service while ensuring theuser's activity.

However, the mobile communication system is gradually expanding not onlythe voice but also the data service, and now it has developed to theextent of providing high-speed data service. However, in a mobilecommunication system in which services are currently being provided, amore advanced mobile communication system is required due to a shortagephenomenon of resources and a high-speed service demand of users.

In recent years, with the explosion of mobile traffic due to the spreadof smart devices, it is becoming difficult to cope with the increasingdata usage for providing cellular communication services using only theexisting licensed frequency spectrums or licensed frequency bands.

In such a situation, a method of using an unlicensed frequency spectrumor an unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band, 6 GHzband, 52.6 GHz or higher band, or the like) for providing cellularcommunication services is being discussed as a solution to the problemof lack of spectrum.

Unlike in licensed bands in which telecommunications carriers secureexclusive use rights through procedures such as auctions, in unlicensedbands, multiple communication devices may be used simultaneously withoutrestrictions on the condition that only a certain level of adjacent bandprotection regulations are observed. For this reason, when an unlicensedband is used for cellular communication service, it is difficult toguarantee the communication quality to the level provided in thelicensed band, and it is likely that interference with existing wirelesscommunication devices (e.g., wireless LAN devices) using the unlicensedband occurs.

In order to use LTE and NR technologies in unlicensed bands, research oncoexistence with existing devices for unlicensed bands and efficientsharing of wireless channels with other wireless communication devicesis to be conducted in advance. That is, it is required to develop arobust coexistence mechanism (RCM) such that devices using LTE and NRtechnologies in the unlicensed band do not affect the existing devicesfor unlicensed bands.

DISCLOSURE Technical Problem

An object of an embodiment of the present invention is to provide achannel access method and a device using the same for performingtransmission in a wireless communication system operating in anunlicensed band.

Technical Solution

According to an embodiment of the present invention, a user equipment(UE) wirelessly communicating with a base station in an unlicensed bandincludes a communication module and a processor controlling thecommunication module. The processor may be configured to receive a grantfor scheduling a plurality of uplink transmissions from the basestation, and when the UE attempts a first fixed duration-based channelaccess for a first transmission which is one of the plurality of uplinktransmissions and fails in the first fixed duration-based channelaccess, may be configured to attempt a second fixed duration-basedchannel access for a second transmission which is a transmissionfollowing the first transmission. The first fixed duration-based channelaccess is a channel access in which, when a channel is sensed to be idlewithin a first fixed duration, the UE performing the first fixedduration-based channel access is allowed to perform a transmissionimmediately after the first fixed duration. The second fixedduration-based channel access is a channel access in which, when thechannel is sensed to be idle within a second fixed duration, the UEperforming the second fixed duration-based channel access is allowed toperform a transmission immediately after the second fixed duration.

The first fixed duration may be shorter than the second fixed duration.

The first fixed duration may be 16 μs, and the second fixed duration maybe 25 μs. The grant may indicate a fixed duration-based channel accessas a channel access type, and indicate a channel access priority used toaccess a channel in which the plurality of uplink transmissions areperformed.

The grant may indicate the first fixed duration-based channel access asthe channel access type.

The grant may include one or more grants for scheduling the plurality ofuplink transmissions, and the plurality of uplink transmissions may becontiguous without a gap in time.

According to an embodiment of the present invention, a base stationwirelessly communicating with a UE in an unlicensed band includes acommunication module and a processor controlling the communicationmodule. The processor may be configured to perform a transmission to theUE immediately after a gap between a transmission of the UE and thetransmission to the UE without sensing within a maximum channeloccupancy time in a channel in which the transmission of the UE isperformed, when a duration of the transmission of the UE is less thanthe maximum channel occupancy time and the gap is not greater than afirst fixed duration. In this case, the first fixed duration is 16 μs.

The processor may be configured to perform the transmission to the UEimmediately after the gap between the transmission of the UE and thetransmission to the UE without sensing within a predetermined durationwhen the gap is not greater than the first fixed duration, and thepredetermined duration may be a constraint applied to the transmissionof the base station separately from the maximum channel occupancy time.

The processor may be configured to attempt a first fixed duration-basedchannel access in a channel in which the transmission of the UE isperformed when the gap between the transmission of the UE and thetransmission to the UE is equal to the first fixed duration. The firstfixed duration-based channel access may be a channel access in which,when the channel is sensed to be idle within a first fixed duration, thebase station performing the first fixed duration-based channel access isallowed to perform an transmission immediately after the first fixedduration.

The processor may be configured to attempt the second fixedduration-based channel access in a channel in which the transmission ofthe UE is performed when the gap between the transmission of the UE andthe transmission to the UE is not greater than the second fixedduration. The second fixed duration-based channel access may be achannel access in which, when the channel is sensed to be idle during asecond fixed duration, the base station performing the first fixedduration-based channel access is allowed to perform a transmissionimmediately after the second fixed duration. In this case, the secondfixed duration is 25 μs.

Channel occupancy including the transmission of the UE and thetransmission of the base station to the UE may be initiated by the basestation.

Channel occupancy including the transmission of the UE and thetransmission of the base station to the UE may be initiated by the UE.

According to an embodiment of the present invention, a method foroperating a UE wirelessly communicating with a base station in theunlicensed band may include: receiving a grant for scheduling aplurality of uplink transmissions from the base station; and when the UEattempts a first fixed duration-based channel access for a firsttransmission which is one of the plurality of uplink transmissions andfails in the first fixed duration-based channel access, attempting asecond fixed duration-based channel access for a second transmissionwhich is a transmission following the first transmission. In this case,the first fixed duration-based channel access may be a channel access inwhich, when the channel is sensed to be idle within a first fixedduration, the UE performing the first fixed duration-based channelaccess is allowed to perform a transmission immediately after the firstfixed duration, and the second fixed duration-based channel access maybe a channel access in which, when the channel is sensed to be idleduring a second fixed duration, the UE performing the second fixedduration-based channel access is allowed to perform a transmissionimmediately after the second fixed duration.

The first fixed duration may be shorter than the second fixed duration.

The first fixed duration may be 16 μs, and the second fixed duration maybe 25 μs.

The grant may indicate a fixed duration-based channel access as achannel access type, and may indicate a channel access priority used toaccess a channel in which the plurality of uplink transmissions areperformed.

The grant may indicate the first fixed duration-based channel access asthe channel access type.

The grant may include one or more grants for scheduling the plurality ofuplink transmissions, and the plurality of uplink transmissions maycontinue without a gap in time.

According to an embodiment of the present invention, a method foroperating a base station wirelessly communicating with a UE in anunlicensed band includes performing a transmission to the UE immediatelyafter a gap between a transmission of the UE and the transmission to theUE without sensing within a maximum channel occupancy time in a channelin which transmission of the UE is performed, when a duration of thetransmission of the UE is less than the maximum channel occupancy timeand the gap is not greater than a first fixed duration. In this case,the first fixed duration is 16 μs.

The method may further include performing the transmission to the UEimmediately after the gap between the transmission of the UE and thetransmission to the UE without sensing within a predetermined durationwhen the gap is not greater than the first fixed duration. In this case,the predetermined duration may be a constraint applied to thetransmission of the base station separately from the maximum channeloccupancy time.

The method may further include attempting the first fixed duration-basedchannel access in a channel in which the transmission of the UE isperformed when the gap between the transmission of the UE and thetransmission to the UE is equal to the first fixed duration. In thiscase, the first fixed duration-based channel access may be a channelaccess in which, when the channel is sensed to be idle within a firstfixed duration, the base station performing the first fixedduration-based channel access is allowed to perform a transmissionimmediately after the first fixed duration.

The method may further include attempting the second fixedduration-based channel access in a channel in which the transmission ofthe UE is performed when the gap between the transmission of the UE andthe transmission to the UE is not greater than the second fixedduration. In this case, the second fixed duration-based channel accessmay be a channel access in which, when the channel is sensed to be idleduring a second fixed duration, the base station performing the secondfixed duration-based channel access is allowed to perform a transmissionimmediately after the second fixed duration. Furthermore, the secondfixed duration may be 25 μs.

Channel occupancy including the transmission of the UE and thetransmission of the base station to the UE may be initiated by the basestation.

Channel occupancy including the transmission of the UE and thetransmission of the base station to the UE may be initiated by the UE.

Advantageous Effects

An embodiment of the present invention provides a channel access methodand a device using the same for performing transmission in a wirelesscommunication system operating in an unlicensed band.

The effect to be achieved by the present invention is not limited to theabove-mentioned effects, and other effects not mentioned will be clearlyunderstood by those of ordinary skill in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a wireless frame structure used in awireless communication system;

FIG. 2 illustrates an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system;

FIG. 3 is a diagram for explaining a physical channel used in a 3GPPsystem and a typical signal transmission method using the physicalchannel;

FIG. 4 illustrates an SS/PBCH block for initial cell access in a 3GPP NRsystem;

FIG. 5 illustrates a procedure for transmitting control information anda control channel in a 3GPP NR system;

FIG. 6 illustrates a control resource set (CORESET) in which a physicaldownlink control channel (PUCCH) may be transmitted in a 3GPP NR system;

FIG. 7 illustrates a method for configuring a PDCCH search space in a3GPP NR system;

FIG. 8 is a conceptual diagram illustrating carrier aggregation;

FIG. 9 is a diagram for explaining signal carrier communication andmultiple carrier communication;

FIG. 10 is a diagram showing an example in which a cross carrierscheduling technique is applied;

FIG. 11 illustrates a code block group (CBG) configuration and timefrequency resource mapping thereof according to an embodiment of thepresent invention.

FIG. 12 illustrates a procedure in which a base station performs aTB-based transmission or a CBG-based transmission, and a UE transmits aHARQ-ACK in response thereto, according to an embodiment of the presentinvention.

FIG. 13 illustrates a New Radio-Unlicensed (NR-U) service environment.

FIG. 14 illustrates an embodiment of an arrangement scenario of a UE anda base station in an NR-U service environment.

FIG. 15 illustrates a communication method (e.g., wireless LAN)operating in an existing unlicensed band.

FIG. 16 illustrates a channel access procedure based on Category 4 LBTaccording to an embodiment of the present invention.

FIG. 17 illustrates an embodiment of a method of adjusting a contentionwindow size (CWS) based on HARQ-ACK feedback.

FIG. 18 is a block diagram illustrating configurations of a UE and abase station according to an embodiment of the present invention.

FIG. 19 illustrates that when a duration of transmission of aninitiating node within a channel occupancy initiated by the initiatingnode does not exceed a maximum occupancy time (MCOT) of the channeloccupancy, a responding node performs a transmission within a channeloccupancy time (COT) initiated by the initiating node, according to anembodiment of the present invention.

FIG. 20 illustrates an operation of a UE when a downlink transmissiondoes not occupy as much as an MCOT within a channel occupancy initiatedby a base station and transmission of the UE is scheduled or configuredby the base station, according to an embodiment of the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “connected” to another element, the elementmay be “directly connected” to the other element or “electricallyconnected” to the other element through a third element. Further, unlessexplicitly described to the contrary, the word “comprise” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements unless otherwise stated. Moreover,limitations such as “more than or equal to” or “less than or equal to”based on a specific threshold may be appropriately substituted with“more than” or “less than”, respectively, in some exemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), and the like. The CDMA may be implemented by a wirelesstechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a wireless technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a wireless technology such as IEEE 802.11 (Wi-Fi),IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP new radio (NR) is a system designedseparately from LTE/LTE-A, and is a system for supporting enhancedmobile broadband (eMBB), ultra-reliable and low latency communication(URLLC), and massive machine type communication (mMTC) services, whichare requirements of IMT-2020. For the clear description, 3GPP NR ismainly described, but the technical idea of the present invention is notlimited thereto.

Unless otherwise specified herein, the base station may include a nextgeneration node B (gNB) defined in 3GPP NR. Furthermore, unlessotherwise specified, a terminal may include a user equipment (UE).Hereinafter, in order to help the understanding of the description, eachcontent is described separately by the embodiments, but each embodimentmay be used in combination with each other. In the presentspecification, the configuration of the UE may indicate a configurationby the base station. In more detail, the base station may configure avalue of a parameter used in an operation of the UE or a wirelesscommunication system by transmitting a channel or a signal to the UE.

FIG. 1 illustrates an example of a wireless frame structure used in awireless communication system.

Referring to FIG. 1, the wireless frame (or radio frame) used in the3GPP NR system may have a length of 10 ms (Δf_(max)N_(f)/100*T_(c)). Inaddition, the wireless frame includes 10 subframes (SFs) having equalsizes. Herein, Δf_(max)=480*10³ Hz, N_(f)=4096,T_(c)=1/(Δf_(ref)*N_(f,ref)), Δf_(ref)=15*10³ Hz, and N_(f,ref)=2048.Numbers from 0 to 9 may be respectively allocated to 10 subframes withinone wireless frame. Each subframe has a length of 1 ms and may includeone or more slots according to a subcarrier spacing. More specifically,in the 3GPP NR system, the subcarrier spacing that may be used is15*2^(μ) kHz, and μ can have a value of μ=0, 1, 2, 3, 4 as subcarrierspacing configuration. That is, 15 kHz, 30 kHz, 60 kHz, 120 kHz and 240kHz may be used for subcarrier spacing. One subframe having a length of1 ms may include 2^(μ) slots. In this case, the length of each slot is2^(−μ) ms. Numbers from 0 to 2^(μ)−1 may be respectively allocated to2^(μ) slots within one wireless frame. In addition, numbers from 0 to10*2^(μ)−1 may be respectively allocated to slots within one subframe.The time resource may be distinguished by at least one of a wirelessframe number (also referred to as a wireless frame index), a subframenumber (also referred to as a subframe index), and a slot number (or aslot index).

FIG. 2 illustrates an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system. In particular, FIG. 2shows the structure of the resource grid of the 3GPP NR system.

There is one resource grid per antenna port. Referring to FIG. 2, a slotincludes a plurality of orthogonal frequency division multiplexing(OFDM) symbols in a time domain and includes a plurality of resourceblocks (RBs) in a frequency domain. An OFDM symbol also means one symbolsection. Unless otherwise specified, OFDM symbols may be referred tosimply as symbols. One RB includes 12 consecutive subcarriers in thefrequency domain. Referring to FIG. 2, a signal transmitted from eachslot may be represented by a resource grid including N^(size,μ)_(grid,x)*N^(RB) _(sc) subcarriers, and N^(slot) _(symb) OFDM symbols.Here, x=DL when the signal is a DL signal, and x=UL when the signal isan UL signal. N^(size,μ) _(grid,x) represents the number of resourceblocks (RBs) according to the subcarrier spacing constituent μ (x is DLor UL), and N^(slot) _(symb) represents the number of OFDM symbols in aslot. N^(RB) _(sc) is the number of subcarriers constituting one RB andN^(RB) _(sc)=12. An OFDM symbol may be referred to as a cyclic shiftOFDM (CP-OFDM) symbol or a discrete Fourier transform spread OFDM(DFT-s-OFDM) symbol according to a multiple access scheme.

The number of OFDM symbols included in one slot may vary according tothe length of a cyclic prefix (CP). For example, in the case of a normalCP, one slot includes 14 OFDM symbols, but in the case of an extendedCP, one slot may include 12 OFDM symbols. In a specific embodiment, theextended CP can only be used at 60 kHz subcarrier spacing. In FIG. 2,for convenience of description, one slot is configured with 14 OFDMsymbols by way of example, but embodiments of the present disclosure maybe applied in a similar manner to a slot having a different number ofOFDM symbols. Referring to FIG. 2, each OFDM symbol includes N^(size,μ)_(grid,x)*N^(RB) _(sc) subcarriers in the frequency domain. The type ofsubcarrier may be divided into a data subcarrier for data transmission,a reference signal subcarrier for transmission of a reference signal,and a guard band. The carrier frequency is also referred to as thecenter frequency (fc).

One RB may be defined by N^(RB) _(sc) (e. g., 12) consecutivesubcarriers in the frequency domain. For reference, a resourceconfigured with one OFDM symbol and one subcarrier may be referred to asa resource element (RE) or a tone. Therefore, one RB can be configuredwith N^(slot) _(symb)*N^(RB) _(sc) resource elements. Each resourceelement in the resource grid can be uniquely defined by a pair ofindexes (k, l) in one slot. k may be an index assigned from 0 toN^(size,μ) _(grid,x)*N^(RB) _(sc)−1 in the frequency domain, and 1 maybe an index assigned from 0 to N^(slot) _(symb)−1 in the time domain.

In order for the UE to receive a signal from the base station or totransmit a signal to the base station, the time/frequency of the UE maybe synchronized with the time/frequency of the base station. This isbecause when the base station and the UE are synchronized, the UE candetermine the time and frequency parameters necessary for demodulatingthe DL signal and transmitting the UL signal at the correct time.

Each symbol of a radio frame used in a time division duplex (TDD) or anunpaired spectrum may be configured with at least one of a DL symbol, anUL symbol, and a flexible symbol. A radio frame used as a DL carrier ina frequency division duplex (FDD) or a paired spectrum may be configuredwith a DL symbol or a flexible symbol, and a radio frame used as a ULcarrier may be configured with a UL symbol or a flexible symbol. In theDL symbol, DL transmission is possible, but UL transmission isimpossible. In the UL symbol, UL transmission is possible, but DLtransmission is impossible. The flexible symbol may be determined to beused as a DL or an UL according to a signal.

Information on the type of each symbol, i.e., information representingany one of DL symbols, UL symbols, and flexible symbols, may beconfigured with a cell-specific or common radio resource control (RRC)signal. In addition, information on the type of each symbol mayadditionally be configured with a UE-specific or dedicated RRC signal.The base station informs, by using cell-specific RRC signals, i) theperiod of cell-specific slot configuration, ii) the number of slots withonly DL symbols from the beginning of the period of cell-specific slotconfiguration, iii) the number of DL symbols from the first symbol ofthe slot immediately following the slot with only DL symbols, iv) thenumber of slots with only UL symbols from the end of the period of cellspecific slot configuration, and v) the number of UL symbols from thelast symbol of the slot immediately before the slot with only the ULsymbol. Here, symbols not configured with any one of a UL symbol and aDL symbol are flexible symbols.

When the information on the symbol type is configured with theUE-specific RRC signal, the base station may signal whether the flexiblesymbol is a DL symbol or an UL symbol in the cell-specific RRC signal.In this case, the UE-specific RRC signal can not change a DL symbol or aUL symbol configured with the cell-specific RRC signal into anothersymbol type. The UE-specific RRC signal may signal the number of DLsymbols among the N^(slot) _(symb) symbols of the corresponding slot foreach slot, and the number of UL symbols among the N^(slot) _(symb)symbols of the corresponding slot. In this case, the DL symbol of theslot may be continuously configured with the first symbol to the i-thsymbol of the slot. In addition, the UL symbol of the slot may becontinuously configured with the j-th symbol to the last symbol of theslot (where i<j). In the slot, symbols not configured with any one of aUL symbol and a DL symbol are flexible symbols.

The type of symbol configured with the above RRC signal may be referredto as a semi-static DL/UL configuration. In the semi-static DL/ULconfiguration previously configured with RRC signals, the flexiblesymbol may be indicated as a DL symbol, an UL symbol, or a flexiblesymbol through dynamic slot format information (SFI) transmitted on aphysical DL control channel (PDCCH). In this case, the DL symbol or ULsymbol configured with the RRC signal is not changed to another symboltype. Table 1 exemplifies the dynamic SFI that the base station canindicate to the UE.

TABLE 1 Symbol number in a slot Symbol number in a slot index 0 1 2 3 45 6 7 8 9 10 11 12 13 index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0 D D D D DD D D D D D D D D 28 D D D D D D D D D D D D X U 1 U U U U U U U U U U UU U U 29 D D D D D D D D D D D X X U 2 X X X X X X X X X X X X X X 30 DD D D D D D D D D X X X U 3 D D D D D D D D D D D D D X 31 D D D D D D DD D D D X U U 4 D D D D D D D D D D D D X X 32 D D D D D D D D D D X X UU 5 D D D D D D D D D D D X X X 33 D D D D D D D D D X X X U U 6 D D D DD D D D D D X X X X 34 D X U U U U U U U U U U U U 7 D D D D D D D D D XX X X X 35 D D X U U U U U U U U U U U 8 X X X X X X X X X X X X X U 36D D D X U U U U U U U U U U 9 X X X X X X X X X X X X U U 37 D X X U U UU U U U U U U U 10 X U U U U U U U U U U U U U 38 D D X X U U U U U U UU U U 11 X X U U U U U U U U U U U U 39 D D D X X U U U U U U U U U 12 XX X U U U U U U U U U U U 40 D X X X U U U U U U U U U U 13 X X X X U UU U U U U U U U 41 D D X X X U U U U U U U U U 14 X X X X X U U U U U UU U U 42 D D D X X X U U U U U U U U 15 X X X X X X U U U U U U U U 43 DD D D D D D D D X X X X U 16 D X X X X X X X X X X X X X 44 D D D D D DX X X X X X U U 17 D D X X X X X X X X X X X X 45 D D D D D D X X U U UU U U 18 D D D X X X X X X X X X X X 46 D D D D D X U D D D D D X U 19 DX X X X X X X X X X X X U 47 D D X U U U U D D X U U U U 20 D D X X X XX X X X X X X U 48 D X U U U U U D X U U U U U 21 D D D X X X X X X X XX X U 49 D D D D X X U D D D D X X U 22 D X X X X X X X X X X X U U 50 DD X X U U U D D X X U U U 23 D D X X X X X X X X X X U U 51 D X X U U UU D X X U U U U 24 D D D X X X X X X X X X U U 52 D X X X X X U D X X XX X U 25 D X X X X X X X X X X U U U 53 D D X X X X U D D X X X X U 26 DD X X X X X X X X X U U U 54 X X X X X X X D D D D D D D 27 D D D X X XX X X X X U U U 55 D D X X X U U U D D D D D D 56-255 Reserved

In Table 1, D denotes a DL symbol, U denotes a UL symbol, and X denotesa flexible symbol. As shown in Table 1, up to two DL/UL switching in oneslot may be allowed.

FIG. 3 is a diagram for explaining a physical channel used in a 3GPPsystem (e.g., NR) and a typical signal transmission method using thephysical channel.

If the power of the UE is turned on or the UE camps on a new cell, theUE performs an initial cell search (S101). Specifically, the UE maysynchronize with the BS in the initial cell search. For this, the UE mayreceive a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS) from the base station to synchronize withthe base station, and obtain information such as a cell ID. Thereafter,the UE can receive the physical broadcast channel from the base stationand obtain the broadcast information in the cell.

Upon completion of the initial cell search, the UE receives a physicaldownlink shared channel (PDSCH) according to the physical downlinkcontrol channel (PDCCH) and information in the PDCCH, so that the UE canobtain more specific system information than the system informationobtained through the initial cell search (S102). Herein, the systeminformation received by the UE is cell-common system information fornormal operating of the UE in a physical layer in radio resource control(RRC) and is referred to remaining system information, or systeminformation block (SIB) 1 is called.

When the UE initially accesses the base station or does not have radioresources for signal transmission (i.e. the UE at RRC IDLE mode), the UEmay perform a random access procedure on the base station (operationsS103 to S106). First, the UE can transmit a preamble through a physicalrandom access channel (PRACH) (S103) and receive a response message forthe preamble from the base station through the PDCCH and thecorresponding PDSCH (S104). When a valid random access response messageis received by the UE, the UE transmits data including the identifier ofthe UE and the like to the base station through a physical uplink sharedchannel (PUSCH) indicated by the UL grant transmitted through the PDCCHfrom the base station (S105). Next, the UE waits for reception of thePDCCH as an indication of the base station for collision resolution. Ifthe UE successfully receives the PDCCH through the identifier of the UE(S106), the random access process is terminated. The UE may obtainUE-specific system information for normal operating of the UE in thephysical layer in RRC layer during a random access process. When the UEobtain the UE-specific system information, the UE enter RRC connectingmode (RRC_CONNECTED mode).

The RRC layer is used for generating or managing message for controllingconnection between the UE and radio access network (RAN). In moredetail, the base station and the UE, in the RRC layer, may performbroadcasting cell system information required by every UE in the cell,managing mobility and handover, measurement report of the UE, storagemanagement including UE capability management and device management. Ingeneral, the RRC signal is not changed and maintained quite longinterval since a period of an update of a signal delivered in the RRClayer is longer than a transmission time interval (TTI) in physicallayer.

After the above-described procedure, the UE receives PDCCH/PDSCH (S107)and transmits a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S108) as a general UL/DL signal transmissionprocedure. In particular, the UE may receive downlink controlinformation (DCI) through the PDCCH. The DCI may include controlinformation such as resource allocation information for the UE. Also,the format of the DCI may vary depending on the intended use. The uplinkcontrol information (UCI) that the UE transmits to the base stationthrough UL includes a DL/UL ACK/NACK signal, a channel quality indicator(CQI), a precoding matrix index (PMI), a rank indicator (RI), and thelike. Here, the CQI, PMI, and RI may be included in channel stateinformation (CSI). In the 3GPP NR system, the UE may transmit controlinformation such as HARQ-ACK and CSI described above through the PUSCHand/or PUCCH.

FIG. 4 illustrates an SS/PBCH block for initial cell access in a 3GPP NRsystem.

When the power is turned on or wanting to access a new cell, the UE mayobtain time and frequency synchronization with the cell and perform aninitial cell search procedure. The UE may detect a physical cellidentity N^(cell) _(ID) of the cell during a cell search procedure. Forthis, the UE may receive a synchronization signal, for example, aprimary synchronization signal (PSS) and a secondary synchronizationsignal (SSS), from a base station, and synchronize with the basestation. In this case, the UE can obtain information such as a cellidentity (ID).

Referring to FIG. 4A, a synchronization signal (SS) will be described inmore detail. The synchronization signal can be classified into PSS andSSS. The PSS may be used to obtain time domain synchronization and/orfrequency domain synchronization, such as OFDM symbol synchronizationand slot synchronization. The SSS can be used to obtain framesynchronization and cell group ID. Referring to FIG. 4A and Table 2, theSS/PBCH block can be configured with consecutive 20 RBs (=240subcarriers) in the frequency axis, and can be configured withconsecutive 4 OFDM symbols in the time axis. In this case, in theSS/PBCH block, the PSS is transmitted in the first OFDM symbol and theSSS is transmitted in the third OFDM symbol through the 56th to 182thsubcarriers. Here, the lowest subcarrier index of the SS/PBCH block isnumbered from 0. In the first OFDM symbol in which the PSS istransmitted, the base station does not transmit a signal through theremaining subcarriers, i.e., 0th to 55th and 183th to 239th subcarriers.In addition, in the third OFDM symbol in which the SSS is transmitted,the base station does not transmit a signal through 48th to 55th and183th to 191th subcarriers. The base station transmits a physicalbroadcast channel (PBCH) through the remaining RE except for the abovesignal in the SS/PBCH block.

TABLE 2 OFDM symbol number l Subcarrier number k Channel relative to thestart relative to the start or signal of an SS/PBCH block of an SS/PBCHblock PSS 0 56, 57, . . . , 182 SSS 2 56, 57, . . . , 182 Set to 0 0 0,1, . . . , 55, 183, 184, . . . , 239 2 48, 49, . . . , 55, 183, 184, . .. , 191 PBCH 1, 3 0, 1, . . . , 239 2 0, 1, . . . , 47, 192, 193, . . ., 239 DM-RS for 1, 3 0 + ν, 4 + ν, PBCH 8 + ν, . . . , 236 + ν 2 0 + ν,4 + ν, 8 + ν, . . . , 44 + ν 192 + ν, 196 + ν, . . . , 236 + ν

The SS allows a total of 1008 unique physical layer cell IDs to begrouped into 336 physical-layer cell-identifier groups, each groupincluding three unique identifiers, through a combination of three PSSsand SSSs, specifically, such that each physical layer cell ID is to beonly a part of one physical-layer cell-identifier group. Therefore, thephysical layer cell ID N^(cell) _(ID)=3N⁽¹⁾ _(ID)+N⁽²⁾ _(ID) can beuniquely defined by the index N⁽¹⁾ _(ID) ranging from 0 to 335indicating a physical-layer cell-identifier group and the index N⁽²⁾_(ID) ranging from 0 to 2 indicating a physical-layer identifier in thephysical-layer cell-identifier group. The UE may detect the PSS andidentify one of the three unique physical-layer identifiers. Inaddition, the UE can detect the SSS and identify one of the 336 physicallayer cell IDs associated with the physical-layer identifier. In thiscase, the sequence d_(PSS)(n) of the PSS is as follows.

d _(PSS)(n)=1−2x(m)

m=(n+43N _(ID) ⁽²⁾)mod 127

0≤n<127

Here, x(i+7)=x(i+4)+x(i))mod 2 and is given as

[x(6) x(5) x(4) x(3) x(2) x(1) x(0)]=[1 1 1 0 1 1 0]

Further, the sequence d_(SSS)(n) of the SSS is as follows.

d_(SSS)(n) = [1 − 2x₀((n + m₀)mod127)][1 − 2x₁((n + m₁)mod127)]$m_{0} = {{15\lfloor \frac{N_{ID}^{(1)}}{112} \rfloor} + {5N_{ID}^{(2)}}}$m₁ = N_(ID)⁽¹⁾mod 112 0 ≤ n < 127 $\begin{matrix}{{Here},{{x_{0}( {i + 7} )} = {( {{x_{0}( {i + 4} )} + {x_{0}(i)}} ){mod}\; 2}}} \\{{x_{1}( {i + 7} )} = {( {{x_{1}( {i + 1} )} + {x_{1}(i)}} ){mod}\; 2}}\end{matrix}$

and is given as

[x ₀(6) x ₀(5) x ₀(4) x ₀(3) x ₀(2) x ₀(1) x ₀(0)]=[0 0 0 0 0 1]

[x ₁(6) x ₁(5) x ₁(4) x ₁(3) x ₁(2) x ₁(1) x ₁(0)]=[0 0 0 0 0 0 1]

A radio frame with a 10 ms length may be divided into two half frameswith a 5 ms length. Referring to FIG. 4B, a description will be made ofa slot in which SS/PBCH blocks are transmitted in each half frame. Aslot in which the SS/PBCH block is transmitted may be any one of thecases A, B, C, D, and E. In the case A, the subcarrier spacing is 15 kHzand the starting time point of the SS/PBCH block is the ({2, 8}+14*n)-thsymbol. In this case, n=0 or 1 at a carrier frequency of 3 GHz or less.In addition, it may be n=0, 1, 2, 3 at carrier frequencies above 3 GHzand below 6 GHz. In the case B, the subcarrier spacing is 30 kHz and thestarting time point of the SS/PBCH block is {4, 8, 16, 20}+28*n. In thiscase, n=0 at a carrier frequency of 3 GHz or less. In addition, it maybe n=0, 1 at carrier frequencies above 3 GHz and below 6 GHz. In thecase C, the subcarrier spacing is 30 kHz and the starting time point ofthe SS/PBCH block is the ({2, 8}+14*n)-th symbol. In this case, n=0 or 1at a carrier frequency of 3 GHz or less. In addition, it may be n=0, 1,2, 3 at carrier frequencies above 3 GHz and below 6 GHz. In the case D,the subcarrier spacing is 120 kHz and the starting time point of theSS/PBCH block is the ({4, 8, 16, 20}+28*n)-th symbol. In this case, at acarrier frequency of 6 GHz or more, n=0, 1, 2, 3, 5, 6, 7, 8, 10, 11,12, 13, 15, 16, 17, 18. In the case E, the subcarrier spacing is 240 kHzand the starting time point of the SS/PBCH block is the ({8, 12, 16, 20,32, 36, 40, 44}+56*n)-th symbol. In this case, at a carrier frequency of6 GHz or more, n=0, 1, 2, 3, 5, 6, 7, 8.

FIG. 5 illustrates a procedure for transmitting control information anda control channel in a 3GPP NR system. Referring to FIG. 5A, the basestation may add a cyclic redundancy check (CRC) masked (e.g., an XORoperation) with a radio network temporary identifier (RNTI) to controlinformation (e.g., downlink control information (DCI)) (S202). The basestation may scramble the CRC with an RNTI value determined according tothe purpose/target of each control information. The common RNTI used byone or more UEs can include at least one of a system information RNTI(SI-RNTI), a paging RNTI (P-RNTI), a random access RNTI (RA-RNTI), and atransmit power control RNTI (TPC-RNTI). In addition, the UE-specificRNTI may include at least one of a cell temporary RNTI (C-RNTI), and theCS-RNTI. Thereafter, the base station may perform rate-matching (S206)according to the amount of resource(s) used for PDCCH transmission afterperforming channel encoding (e.g., polar coding) (S204). Thereafter, thebase station may multiplex the DCI(s) based on the control channelelement (CCE) based PDCCH structure (S208). In addition, the basestation may apply an additional process (S210) such as scrambling,modulation (e.g., QPSK), interleaving, and the like to the multiplexedDCI(s), and then map the DCI(s) to the resource to be transmitted. TheCCE is a basic resource unit for the PDCCH, and one CCE may include aplurality (e.g., six) of resource element groups (REGs). One REG may beconfigured with a plurality (e.g., 12) of REs. The number of CCEs usedfor one PDCCH may be defined as an aggregation level. In the 3GPP NRsystem, an aggregation level of 1, 2, 4, 8, or 16 may be used. FIG. 5Bis a diagram related to a CCE aggregation level and the multiplexing ofa PDCCH and illustrates the type of a CCE aggregation level used for onePDCCH and CCE(s) transmitted in the control area according thereto.

FIG. 6 illustrates a control resource set (CORESET) in which a physicaldownlink control channel (PUCCH) may be transmitted in a 3GPP NR system.

The CORESET is a time-frequency resource in which PDCCH, that is, acontrol signal for the UE, is transmitted. In addition, a search spaceto be described later may be mapped to one CORESET. Therefore, the UEmay monitor the time-frequency domain designated as CORESET instead ofmonitoring all frequency bands for PDCCH reception, and decode the PDCCHmapped to CORESET. The base station may configure one or more CORESETsfor each cell to the UE. The CORESET may be configured with up to threeconsecutive symbols on the time axis. In addition, the CORESET may beconfigured in units of six consecutive PRBs on the frequency axis. Inthe embodiment of FIG. 5, CORESET #1 is configured with consecutivePRBs, and CORESET #2 and CORESET #3 are configured with discontinuousPRBs. The CORESET can be located in any symbol in the slot. For example,in the embodiment of FIG. 5, CORESET #1 starts at the first symbol ofthe slot, CORESET #2 starts at the fifth symbol of the slot, and CORESET#9 starts at the ninth symbol of the slot.

FIG. 7 illustrates a method for setting a PUCCH search space in a 3GPPNR system.

In order to transmit the PDCCH to the UE, each CORESET may have at leastone search space. In the embodiment of the present disclosure, thesearch space is a set of all time-frequency resources (hereinafter,PDCCH candidates) through which the PDCCH of the UE is capable of beingtransmitted. The search space may include a common search space that theUE of the 3GPP NR is required to commonly search and a UE-specific or aUE-specific search space that a specific UE is required to search. Inthe common search space, UE may monitor the PDCCH that is set so thatall UEs in the cell belonging to the same base station commonly search.In addition, the UE-specific search space may be set for each UE so thatUEs monitor the PDCCH allocated to each UE at different search spaceposition according to the UE. In the case of the UE-specific searchspace, the search space between the UEs may be partially overlapped andallocated due to the limited control area in which the PDCCH may beallocated. Monitoring the PDCCH includes blind decoding for PDCCHcandidates in the search space. When the blind decoding is successful,it may be expressed that the PDCCH is (successfully) detected/receivedand when the blind decoding fails, it may be expressed that the PDCCH isnot detected/not received, or is not successfully detected/received.

For convenience of explanation, a PDCCH scrambled with a group common(GC) RNTI previously known to one or more UEs so as to transmit DLcontrol information to the one or more UEs is referred to as a groupcommon (GC) PDCCH or a common PDCCH. In addition, a PDCCH scrambled witha specific-terminal RNTI that a specific UE already knows so as totransmit UL scheduling information or DL scheduling information to thespecific UE is referred to as a specific-UE PDCCH. The common PDCCH maybe included in a common search space, and the UE-specific PDCCH may beincluded in a common search space or a UE-specific PDCCH.

The base station may signal each UE or UE group through a PDCCH aboutinformation (i.e., DL Grant) related to resource allocation of a pagingchannel (PCH) and a downlink-shared channel (DL-SCH) that are atransmission channel or information (i.e., UL grant) related to resourceallocation of a uplink-shared channel (UL-SCH) and a hybrid automaticrepeat request (HARD). The base station may transmit the PCH transportblock and the DL-SCH transport block through the PDSCH. The base stationmay transmit data excluding specific control information or specificservice data through the PDSCH. In addition, the UE may receive dataexcluding specific control information or specific service data throughthe PDSCH.

The base station may include, in the PDCCH, information on to which UE(one or a plurality of UEs) PDSCH data is transmitted and how the PDSCHdata is to be received and decoded by the corresponding UE, and transmitthe PDCCH. For example, it is assumed that the DCI transmitted on aspecific PDCCH is CRC masked with an RNTI of “A”, and the DCI indicatesthat PDSCH is allocated to a radio resource (e.g., frequency location)of “B” and indicates transmission format information (e.g., transportblock size, modulation scheme, coding information, etc.) of “C”. The UEmonitors the PDCCH using the RNTI information that the UE has. In thiscase, if there is a UE which performs blind decoding the PDCCH using the“A” RNTI, the UE receives the PDCCH, and receives the PDSCH indicated by“B” and “C” through the received PDCCH information.

Table 3 shows an embodiment of a physical uplink control channel (PUCCH)used in a wireless communication system.

TABLE 3 PUCCH format Length in OFDM symbols Number of bits 0 1-2  ≤2 14-14 ≤2 2 1-2  >2 3 4-14 >2 4 4-14 >2

The PUCCH may be used to transmit the following UL control information(UCI).

-   -   Scheduling Request (SR): Information used for requesting a UL        UL-SCH resource.    -   HARQ-ACK: A Response to PDCCH (indicating DL SPS release) and/or        a response to DL transport block (TB) on PDSCH. HARQ-ACK        indicates whether information successfully transmitted on the        PDCCH or PDSCH is received. The HARQ-ACK response includes        positive ACK (simply ACK), negative ACK (hereinafter NACK),        Discontinuous Transmission (DTX), or NACK/DTX. Here, the term        HARQ-ACK is used mixed with HARQ-ACK/NACK and ACK/NACK. In        general, ACK may be represented by bit value 1 and NACK may be        represented by bit value 0.    -   Channel State Information (CSI): Feedback information on the DL        channel. The UE generates it based on the CSI-Reference Signal        (RS) transmitted by the base station. Multiple Input Multiple        Output (MIMO)-related feedback information includes a Rank        Indicator (RI) and a Precoding Matrix Indicator (PMI). CSI can        be divided into CSI part 1 and CSI part 2 according to the        information indicated by CSI.

In the 3GPP NR system, five PUCCH formats may be used to support variousservice scenarios, various channel environments, and frame structures.

PUCCH format 0 is a format capable of delivering 1-bit or 2-bit HARQ-ACKinformation or SR. PUCCH format 0 can be transmitted through one or twoOFDM symbols on the time axis and one PRB on the frequency axis. WhenPUCCH format 0 is transmitted in two OFDM symbols, the same sequence onthe two symbols may be transmitted through different RBs. In this case,the sequence may be a sequence cyclic shifted (CS) from a base sequenceused in PUCCH format 0. Through this, the UE may obtain a frequencydiversity gain. In more detail, the UE may determine a cyclic shift (CS)value m_(cs) according to M_(bit) bit UCI (M_(bit)=1 or 2). In addition,the base sequence having the length of 12 may be transmitted by mappinga cyclic shifted sequence based on a predetermined CS value m_(cs) toone OFDM symbol and 12 REs of one RB. When the number of cyclic shiftsavailable to the UE is 12 and M_(bit)=1, 1 bit UCI 0 and 1 may be mappedto two cyclic shifted sequences having a difference of 6 in the cyclicshift value, respectively. In addition, when M_(bit)=2, 2 bit UCI 00,01, 11, and 10 may be mapped to four cyclic shifted sequences having adifference of 3 in cyclic shift values, respectively.

PUCCH format 1 may deliver 1-bit or 2-bit HARQ-ACK information or SR.PUCCH format 1 maybe transmitted through consecutive OFDM symbols on thetime axis and one PRB on the frequency axis. Here, the number of OFDMsymbols occupied by PUCCH format 1 may be one of 4 to 14. Morespecifically, UCI, which is M_(bit)=1, may be BPSK-modulated. The UE maymodulate UCI, which is M_(bit)=2, with quadrature phase shift keying(QPSK). A signal is obtained by multiplying a modulated complex valuedsymbol d(0) by a sequence of length 12. In this case, the sequence maybe a base sequence used for PUCCH format 0. The UE spreads theeven-numbered OFDM symbols to which PUCCH format 1 is allocated throughthe time axis orthogonal cover code (OCC) to transmit the obtainedsignal. PUCCH format 1 determines the maximum number of different UEsmultiplexed in the one RB according to the length of the OCC to be used.A demodulation reference signal (DMRS) may be spread with OCC and mappedto the odd-numbered OFDM symbols of PUCCH format 1.

PUCCH format 2 may deliver UCI exceeding 2 bits. PUCCH format 2 may betransmitted through one or two OFDM symbols on the time axis and one ora plurality of RBs on the frequency axis. When PUCCH format 2 istransmitted in two OFDM symbols, the sequences which are transmitted indifferent RBs through the two OFDM symbols may be same each other. Here,the sequence may be a plurality of modulated complex valued symbolsd(0), . . . , d(M_(symbol)−1). Here, M_(symbol) may be M_(bit)/2.Through this, the UE may obtain a frequency diversity gain. Morespecifically, M_(bit) bit UCI (M_(bit)>2) is bit-level scrambled, QPSKmodulated, and mapped to RB(s) of one or two OFDM symbol(s). Here, thenumber of RBs may be one of 1 to 16.

PUCCH format 3 or PUCCH format 4 may deliver UCI exceeding 2 bits. PUCCHformat 3 or PUCCH format 4 may be transmitted through consecutive OFDMsymbols on the time axis and one PRB on the frequency axis. The numberof OFDM symbols occupied by PUCCH format 3 or PUCCH format 4 may be oneof 4 to 14. Specifically, the UE modulates M_(bit) bits UCI (Mbit>2)with π/2-Binary Phase Shift Keying (BPSK) or QPSK to generate a complexvalued symbol d(0) to d(M_(symb)−1). Here, when using π/2-BPSK,M_(symb)=M_(bit), and when using QPSK, M_(symb)=M_(bit)/2. The UE maynot apply block-unit spreading to the PUCCH format 3. However, the UEmay apply block-unit spreading to one RB (i.e., 12 subcarriers) usingPreDFT-OCC of a length of 12 such that PUCCH format 4 may have two orfour multiplexing capacities. The UE performs transmit precoding (orDFT-precoding) on the spread signal and maps it to each RE to transmitthe spread signal.

In this case, the number of RBs occupied by PUCCH format 2, PUCCH format3, or PUCCH format 4 may be determined according to the length andmaximum code rate of the UCI transmitted by the UE. When the UE usesPUCCH format 2, the UE may transmit HARQ-ACK information and CSIinformation together through the PUCCH. When the number of RBs that theUE may transmit is greater than the maximum number of RBs that PUCCHformat 2, or PUCCH format 3, or PUCCH format 4 may use, the UE maytransmit only the remaining UCI information without transmitting someUCI information according to the priority of the UCI information.

PUCCH format 1, PUCCH format 3, or PUCCH format 4 may be configuredthrough the RRC signal to indicate frequency hopping in a slot. Whenfrequency hopping is configured, the index of the RB to be frequencyhopped may be configured with an RRC signal. When PUCCH format 1, PUCCHformat 3, or PUCCH format 4 is transmitted through N OFDM symbols on thetime axis, the first hop may have floor (N/2) OFDM symbols and thesecond hop may have ceiling(N/2) OFDM symbols.

PUCCH format 1, PUCCH format 3, or PUCCH format 4 may be configured tobe repeatedly transmitted in a plurality of slots. In this case, thenumber K of slots in which the PUCCH is repeatedly transmitted may beconfigured by the RRC signal. The repeatedly transmitted PUCCHs muststart at an OFDM symbol of the constant position in each slot, and havethe constant length. When one OFDM symbol among OFDM symbols of a slotin which a UE should transmit a PUCCH is indicated as a DL symbol by anRRC signal, the UE may not transmit the PUCCH in a corresponding slotand delay the transmission of the PUCCH to the next slot to transmit thePUCCH.

Meanwhile, in the 3GPP NR system, a UE may performtransmission/reception using a bandwidth equal to or less than thebandwidth of a carrier (or cell). For this, the UE may receive theBandwidth part (BWP) configured with a continuous bandwidth of some ofthe carrier's bandwidth. A UE operating according to TDD or operating inan unpaired spectrum can receive up to four DL/UL BWP pairs in onecarrier (or cell). In addition, the UE may activate one DL/UL BWP pair.A UE operating according to FDD or operating in paired spectrum canreceive up to four DL BWPs on a DL carrier (or cell) and up to four ULBWPs on a UL carrier (or cell). The UE may activate one DL BWP and oneUL BWP for each carrier (or cell). The UE may not perform reception ortransmission in a time-frequency resource other than the activated BWP.The activated BWP may be referred to as an active BWP.

The base station may indicate the activated BWP among the BWPsconfigured by the UE through downlink control information (DCI). The BWPindicated through the DCI is activated and the other configured BWP(s)are deactivated. In a carrier (or cell) operating in TDD, the basestation may include, in the DCI for scheduling PDSCH or PUSCH, abandwidth part indicator (BPI) indicating the BWP to be activated tochange the DL/UL BWP pair of the UE. The UE may receive the DCI forscheduling the PDSCH or PUSCH and may identify the DL/UL BWP pairactivated based on the BPI. For a DL carrier (or cell) operating in anFDD, the base station may include a BPI indicating the BWP to beactivated in the DCI for scheduling PDSCH so as to change the DL BWP ofthe UE. For a UL carrier (or cell) operating in an FDD, the base stationmay include a BPI indicating the BWP to be activated in the DCI forscheduling PUSCH so as to change the UL BWP of the UE.

FIG. 8 is a conceptual diagram illustrating carrier aggregation.

The carrier aggregation is a method in which the UE uses a plurality offrequency blocks or cells (in the logical sense) configured with ULresources (or component carriers) and/or DL resources (or componentcarriers) as one large logical frequency band in order for a wirelesscommunication system to use a wider frequency band. One componentcarrier may also be referred to as a term called a Primary cell (PCell)or a Secondary cell (SCell), or a Primary SCell (PScell). However,hereinafter, for convenience of description, the term “componentcarrier” is used.

Referring to FIG. 8, as an example of a 3GPP NR system, the entiresystem band may include up to 16 component carriers, and each componentcarrier may have a bandwidth of up to 400 MHz. The component carrier mayinclude one or more physically consecutive subcarriers. Although it isshown in FIG. 8 that each of the component carriers has the samebandwidth, this is merely an example, and each component carrier mayhave a different bandwidth. Also, although each component carrier isshown as being adjacent to each other in the frequency axis, thedrawings are shown in a logical concept, and each component carrier maybe physically adjacent to one another, or may be spaced apart.

Different center frequencies may be used for each component carrier.Also, one common center frequency may be used in physically adjacentcomponent carriers. Assuming that all the component carriers arephysically adjacent in the embodiment of FIG. 8, center frequency A maybe used in all the component carriers. Further, assuming that therespective component carriers are not physically adjacent to each other,center frequency A and the center frequency B can be used in each of thecomponent carriers.

When the total system band is extended by carrier aggregation, thefrequency band used for communication with each UE can be defined inunits of a component carrier. UE A may use 100 MHz, which is the totalsystem band, and performs communication using all five componentcarriers. UEs B₁˜B₅ can use only a 20 MHz bandwidth and performcommunication using one component carrier. UEs C₁ and C₂ may use a 40MHz bandwidth and perform communication using two component carriers,respectively. The two component carriers may be logically/physicallyadjacent or non-adjacent. UE C₁ represents the case of using twonon-adjacent component carriers, and UE C₂ represents the case of usingtwo adjacent component carriers.

FIG. 9 is a drawing for explaining signal carrier communication andmultiple carrier communication. Particularly, FIG. 9A shows a singlecarrier subframe structure and FIG. 9B shows a multi-carrier subframestructure.

Referring to FIG. 9A, in an FDD mode, a general wireless communicationsystem may perform data transmission or reception through one DL bandand one UL band corresponding thereto. In another specific embodiment,in a TDD mode, the wireless communication system may divide a radioframe into a UL time unit and a DL time unit in a time domain, andperform data transmission or reception through a UL/DL time unit.Referring to FIG. 9B, three 20 MHz component carriers (CCs) can beaggregated into each of UL and DL, so that a bandwidth of 60 MHz can besupported. Each CC may be adjacent or non-adjacent to one another in thefrequency domain. FIG. 9B shows a case where the bandwidth of the UL CCand the bandwidth of the DL CC are the same and symmetric, but thebandwidth of each CC can be determined independently. In addition,asymmetric carrier aggregation with different number of UL CCs and DLCCs is possible. A DL/UL CC allocated/configured to a specific UEthrough RRC may be called as a serving DL/UL CC of the specific UE.

The base station may perform communication with the UE by activatingsome or all of the serving CCs of the UE or deactivating some CCs. Thebase station can change the CC to be activated/deactivated, and changethe number of CCs to be activated/deactivated. If the base stationallocates a CC available for the UE as to be cell-specific orUE-specific, at least one of the allocated CCs can be deactivated,unless the CC allocation for the UE is completely reconfigured or the UEis handed over. One CC that is not deactivated by the UE is called as aPrimary CC (PCC) or a primary cell (PCell), and a CC that the basestation can freely activate/deactivate is called as a Secondary CC (SCC)or a secondary cell (SCell).

Meanwhile, 3GPP NR uses the concept of a cell to manage radio resources.A cell is defined as a combination of DL resources and UL resources,that is, a combination of DL CC and UL CC. A cell may be configured withDL resources alone, or a combination of DL resources and UL resources.When the carrier aggregation is supported, the linkage between thecarrier frequency of the DL resource (or DL CC) and the carrierfrequency of the UL resource (or UL CC) may be indicated by systeminformation. The carrier frequency refers to the center frequency ofeach cell or CC. A cell corresponding to the PCC is referred to as aPCell, and a cell corresponding to the SCC is referred to as an SCell.The carrier corresponding to the PCell in the DL is the DL PCC, and thecarrier corresponding to the PCell in the UL is the UL PCC. Similarly,the carrier corresponding to the SCell in the DL is the DL SCC and thecarrier corresponding to the SCell in the UL is the UL SCC. According toUE capability, the serving cell(s) may be configured with one PCell andzero or more SCells. In the case of UEs that are in the RRC_CONNECTEDstate but not configured for carrier aggregation or that do not supportcarrier aggregation, there is only one serving cell configured only withPCell.

As mentioned above, the term “cell” used in carrier aggregation isdistinguished from the term “cell” which refers to a certaingeographical area in which a communication service is provided by onebase station or one antenna group. That is, one component carrier mayalso be referred to as a scheduling cell, a scheduled cell, a primarycell (PCell), a secondary cell (SCell), or a primary SCell (PScell).However, in order to distinguish between a cell referring to a certaingeographical area and a cell of carrier aggregation, in the presentdisclosure, a cell of a carrier aggregation is referred to as a CC, anda cell of a geographical area is referred to as a cell.

FIG. 10 is a diagram showing an example in which a cross carrierscheduling technique is applied. When cross carrier scheduling is set,the control channel transmitted through the first CC may schedule a datachannel transmitted through the first CC or the second CC using acarrier indicator field (CIF). The CIF is included in the DCI. In otherwords, a scheduling cell is set, and the DL grant/UL grant transmittedin the PDCCH area of the scheduling cell schedules the PDSCH/PUSCH ofthe scheduled cell. That is, a search area for the plurality ofcomponent carriers exists in the PDCCH area of the scheduling cell. APCell may be basically a scheduling cell, and a specific SCell may bedesignated as a scheduling cell by an upper layer.

In the embodiment of FIG. 10, it is assumed that three DL CCs aremerged. Here, it is assumed that DL component carrier #0 is DL PCC (orPCell), and DL component carrier #1 and DL component carrier #2 are DLSCCs (or SCell). In addition, it is assumed that the DL PCC is set tothe PDCCH monitoring CC. When cross-carrier scheduling is not configuredby UE-specific (or UE-group-specific or cell-specific) higher layersignaling, a CIF is disabled, and each DL CC can transmit only a PDCCHfor scheduling its PDSCH without the CIF according to an NR PDCCH rule(non-cross-carrier scheduling, self-carrier scheduling). Meanwhile, ifcross-carrier scheduling is configured by UE-specific (orUE-group-specific or cell-specific) higher layer signaling, a CIF isenabled, and a specific CC (e.g., DL PCC) may transmit not only thePDCCH for scheduling the PDSCH of the DL CC A using the CIF but also thePDCCH for scheduling the PDSCH of another CC (cross-carrier scheduling).On the other hand, a PDCCH is not transmitted in another DL CC.Accordingly, the UE monitors the PDCCH not including the CIF to receivea self-carrier scheduled PDSCH depending on whether the cross-carrierscheduling is configured for the UE, or monitors the PDCCH including theCIF to receive the cross-carrier scheduled PDSCH.

On the other hand, FIGS. 9 and 10 illustrate the subframe structure ofthe 3GPP LTE-A system, and the same or similar configuration may beapplied to the 3GPP NR system. However, in the 3GPP NR system, thesubframes of FIGS. 9 and 10 may be replaced with slots.

FIG. 11 illustrates a code block group (CBG) configuration and timefrequency resource mapping thereof according to an embodiment of thepresent invention. More specifically, FIG. 11(a) illustrates anembodiment of a CBG configuration included in one transport block (TB),and FIG. 11(b) illustrates a time-frequency resource mapping of the CBGconfiguration.

A channel code defines the maximum supported length. For example, themaximum supported length of the turbo code used in 3GPP LTE (-A) is 6144bits. However, the length of a transport block (TB) transmitted on thePDSCH may be longer than 6144 bits. If the length of the TB is longerthan the maximum supported length, the TB may be divided into codeblocks (CBs) having a maximum length of 6144 bits. Each CB is a unit inwhich channel coding is performed. Additionally, for efficientretransmission, several CBs may be grouped to configure one CBG. The UEand the base station require information on how the CBG is configured.

The CBG and the CB within the TB may be configured according to variousembodiments. According to an embodiment, the number of available CBGsmay be determined as a fixed value, or may be configured with RRCconfiguration information between the base station and the UE. In thiscase, the number of CBs is determined with the length of the TB, and theCBG may be configured depending on the information on the determinednumber. According to another embodiment, the number of CBs to beincluded in one CBG may be determined as a fixed value, or may beconfigured with RRC configuration information between the base stationand the UE. In this case, if the number of CBs is determined with thelength of the TB, the number of the CBGs may be configured depending onthe information on the number of CBs per CBG.

Referring to the embodiment of FIG. 11(a), one TB may be divided intoeight CBs. Eight CBs may be grouped into four CBGs again. The mappingrelationship between the CBs and the CBGs (or CBG configuration) may beconfigured as static between the base station and the UE, or may beestablished as semi-static with RRC configuration information. Accordingto another embodiment, the mapping relationship may be configuredthrough dynamic signaling. When the UE receives the PDCCH transmitted bythe base station, the UE may directly or indirectly identify the mappingrelationship between the CB and the CBG (or CBG configuration) throughexplicit information and/or implicit information. One CBG may includeonly one CB, or may include all CBs constituting one TB. For reference,the techniques presented in the embodiments of the present invention maybe applied regardless of the configuration of the CB and the CBG.

Referring to FIG. 11(b), CBGs constituting one TB are mapped totime-frequency resources for which the PDSCH is scheduled. According toan embodiment, each of the CBGs may be allocated first on the frequencyaxis and then extended on the time axis. When a PDSCH consisting of oneTB including four CBGs is allocated to seven OFDM symbols, CBG0 may betransmitted over the first and second OFDM symbols, CBG1 may betransmitted over the second, third, and fourth OFDM symbols, CBG2 may betransmitted over the fourth, fifth, and sixth OFDM symbols, and CBG3 maybe transmitted over the sixth and seventh OFDM symbols. Thetime-frequency mapping relationship allocated with the CBG and PDSCH maybe determined between the base station and the UE. However, the mappingrelationship illustrated in FIG. 11(b) is an embodiment for describingthe present invention, and the techniques presented in the embodiment ofthe present invention may be applied regardless of the time-frequencymapping relationship of the CBG.

FIG. 12 illustrates a procedure in which a base station performs aTB-based transmission or a CBG-based transmission, and a UE transmits aHARQ-ACK in response thereto. Referring to FIG. 12, the base station mayconfigure a transmission scheme suitable for the UE of the TB-basedtransmission and the CBG-based transmission. The UE may transmitHARQ-ACK information bit(s) according to the transmission schemeconfigured by the base station through the PUCCH or PUSCH. The basestation may configure the PDCCH to schedule the PDSCH to be transmittedto the UE. The PDCCH may schedule the TB-based transmission and/or theCBG-based transmission. For example, one TB or two TBs may be scheduledon the PDCCH. If one TB is scheduled, the UE has to feedback 1-bitHARQ-ACK. If two TBs are scheduled, a 2-bit HARQ-ACK has to be fed backfor each of the two TBs. In order to eliminate ambiguity between thebase station and the UE, a predetermined order may exist between eachinformation bit of the 2-bit HARQ-ACK and two TBs. For reference, whenthe MIMO transmission rank or layer is low, one TB may be transmitted onone PDSCH, and when the MIMO transmission rank or layer is high, two TBsmay be transmitted on one PDSCH.

The UE may transmit a 1-bit TB-based HARQ-ACK per one TB to inform thebase station whether or not the reception of each TB is successful. Inorder to generate a HARQ-ACK for one TB, the UE may check the receptionerror of the TB through a TB-CRC. When the TB-CRC for the TB issuccessfully checked, the UE generates an ACK for the HARQ-ACK of theTB. However, if a TB-CRC error for the TB occurs, the UE generates aNACK for the HARQ-ACK of the TB. The UE transmits TB-based HARQ-ACK(s)generated as described above to the base station. The base stationretransmits the TB of response with a NACK, among the TB-basedHARQ-ACK(s) received from the UE.

In addition, the UE may transmit a 1-bit CBG-based HARQ-ACK per one CBGto inform the base station whether or not the reception of each CBG issuccessful. In order to generate a HARQ-ACK for one CBG, the UE maydecode all CBs included in the CBG and check the reception error of eachCB through the CB-CRC. When the UE successfully receives all CBsconstituting one CBG (that is, when all CB-CRCs are successfullychecked), the UE generates an ACK for the HARQ-ACK of the CBG. However,when the UE does not successfully receive at least one of the CBsconstituting one CBG (that is, when at least one CB-CRC error occurs),the UE generates a NACK for the HARQ-ACK of the CBG. The UE transmitsthe CBG-based HARQ-ACK(s) generated as described above to the basestation. The base station retransmits the CBG of response with a NACK,among the CBG-based HARQ-ACK(s) received from the UB. According to anembodiment, the CB configuration of the retransmitted CBG may be thesame as the CB configuration of the previously transmitted CBG. Thelength of the CBG-based HARQ-ACK information bit(s) transmitted by theUE to the base station may be determined based on the number of CBGstransmitted through the PDSCH or the maximum number of CBGs configuredwith RRC signals.

On the other hand, even when the UE successfully receives all the CBGsincluded in the TB, a TB-CRC error for the TB may occur. In this case,the UE may perform flipping of the CBG-based HARQ-ACK in order torequest retransmission for the TB. That is, even though all CBGsincluded in the TB are successfully received, the UE may generate all ofthe CBG-based HARQ-ACK information bits as NACKs. Upon receiving theCBG-based HARQ-ACK feedback in which all HARQ-ACK information bits areNACKs, the base station retransmits all CBGs of the TB.

According to an embodiment of the present invention, CBG-based HARQ-ACKfeedback may be used for the successful transmission of the TB. The basestation may indicate the UE to transmit a CBG-based HARQ-ACK. In thiscase, a retransmission technique according to the CBG-based HARQ-ACK maybe used. The CBG-based HARQ-ACK may be transmitted through a PUCCH. Inaddition, when the UCI is configured to be transmitted through thePUSCH, the CBG-based HARQ-ACK may be transmitted through the PUSCH. Inthe PUCCH, the configuration of the HARQ-ACK resource may be configuredthrough an RRC signal. In addition, an actually transmitted HARQ-ACKresource may be indicated through a PDCCH scheduling a PDSCH transmittedbased on the CBG. The UE may transmit HARQ-ACK(s) for whether or not thereception of transmitted CBGs is transmitted, through one PUCCH resourceindicated through the PDCCH among PUCCH resources configured with RRC.

The base station may identify whether the UE has successfully receivedthe CBG(s) transmitted to the UE through CBG-based HARQ-ACK feedback ofthe UE. That is, through the HARQ-ACK for each CBG received from the UE,the base station may recognize the CBG(s) that the UE has successfullyreceived and the CBG(s) that the UE has failed to receive. The basestation may perform CBG retransmission based on the received CBG-basedHARQ-ACK. More specifically, the base station may bundle and retransmitonly the CBG(s) of HARQ-ACKs of response with failure, in one TB. Inthis case, the CBG(s) for which the HARQ-ACKs is responded withsuccessful reception are excluded from retransmission. The base stationmay schedule the retransmitted CBG(s) as one PDSCH and transmit it tothe UE.

<Communication Method in Unlicensed Band>

FIG. 13 illustrates a New Radio-Unlicensed (NR-U) service environment.

Referring to FIG. 13, a service environment in which NR technology 11 inthe existing licensed band and NR-Unlicensed (NR-U), i.e., NR technology12 in the unlicensed band may be provide to the user. For example, inthe NR-U environment, NR technology 11 in the licensed band and the NRtechnology 21 in the unlicensed band may be integrated usingtechnologies such as carrier aggregation which may contribute to networkcapacity expansion. In addition, in an asymmetric traffic structure withmore downlink data than uplink data, NR-U can provide an NR serviceoptimized for various needs or environments. For convenience, the NRtechnology in the licensed band is referred to as NR-L (NR-Licensed),and the NR technology in the unlicensed band is referred to as NR-U(NR-Unlicensed).

FIG. 14 illustrates a deployment scenario of a user equipment and a basestation in an NR-U service environment. A frequency band targeted by theNR-U service environment has short radio communication range due to thehigh frequency characteristics. Considering this, the deploymentscenario of the user equipment and the base station may be an overlaymodel or a co-located model in an environment in which coexist theexisting NR-L service and NR-U service.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theNR-U service as an auxiliary downlink channel of the NR-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the NR-L service and the NR-U serviceto downlink transmission. A coverage (33) of the NR-L service and acoverage (34) of the NR-U service may be different according to thefrequency band, transmission power, and the like.

When NR communication is performed in the unlicensed band, conventionalequipments (e.g., wireless LAN (Wi-Fi) equipments) which performcommunication in the corresponding unlicensed band may not demodulate anNR-U message or data. Therefore, conventional equipments determine theNR-U message or data as a kind of energy to perform an interferenceavoidance operation by an energy detection technique. That is, whenenergy corresponding to the NR-U message or data is lower than −62 dBmor certain energy detection (ED) threshold value, the wireless LANequipments may perform communication by disregarding the correspondingmessage or data. As a result, that user equipment which performs the NRcommunication in the unlicensed band may be frequently interfered by thewireless LAN equipments.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an NR-Utechnology/service. However, since peripheral equipments which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficient NR-Uservice is difficult. Therefore, a research into a coexistence schemewith the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the NR-U technology. That is, a robust coexistencemechanism in which the NR-U device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 15 illustrates a conventional communication scheme (e.g., wirelessLAN) operating in an unlicensed band. Since most devices that operate inthe unlicensed band operate based on listen-before-talk (LBT), a clearchannel assessment (CCA) technique that senses a channel before datatransmission is performed.

Referring to FIG. 15, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel. Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a backoff procedure after a defer duration(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer duration represents a minimum time when the terminalneeds to wait after the channel is idle. The backoff procedure allowsthe terminal to further wait for a predetermined time after the deferduration. For example, the terminal stands by while decreasing a slottime for slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is idle, and aterminal that completely exhausts the slot time may attempt to accessthe corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel. When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the backoff procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since the existing communication in the unlicensedband mostly operates based on LBT, a channel access in the NR-U systemalso performs LBT for coexistence with existing devices. Specifically,the channel access method on the unlicensed band in the NR may beclassified into the following four categories according to thepresence/absence of LBT/application method.

Category 1: No LBT

-   -   The Tx entity does not perform the LBT procedure for        transmission.

Category 2: LBT without Random Backoff

-   -   The Tx entity senses whether a channel is idle during a first        interval without random backoff to perform a transmission. That        is, the Tx entity may perform a transmission through the channel        immediately after the channel is sensed to be idle during the        first interval. The first interval is an interval of a        predetermined length immediately before the Tx entity performs        the transmission. According to an embodiment, the first interval        may be an interval of 25 μs length, but the present invention is        not limited thereto.

Category 3: LBT Performing Random Backoff Using CW of Fixed Size

-   -   The Tx entity obtains a random value within the CW of the fixed        size, sets it to an initial value of a backoff counter (or        backoff timer) N, and performs backoff by using the set backoff        counter N. That is, in the backoff procedure, the Tx entity        decreases the backoff counter by 1 whenever the channel is        sensed to be idle for a predetermined slot period. Here, the        predetermined slot period may be 9 μs, but the present invention        is not limited thereto. The backoff counter N is decreased by 1        from the initial value, and when the value of the backoff        counter N reaches 0, the Tx entity may perform the transmission.        Meanwhile, in order to perform backoff, the Tx entity first        senses whether the channel is idle during a second interval        (that is, a defer duration T_(d)). According to an embodiment of        the present invention, the Tx entity may sense (determine)        whether the channel is idle during the second interval,        according to whether the channel is idle for at least some        period (e.g., one slot period) within the second interval. The        second interval may be set based on the channel access priority        class of the Tx entity, and consists of a period of 16 us and m        consecutive slot periods. Here, m is a value set according to        the channel access priority class. The Tx entity performs        channel sensing to decrease the backoff counter when the channel        is sensed to be idle during the second interval. On the other        hand, when the channel is sensed to be busy during the backoff        procedure, the backoff procedure is stopped. After stopping the        backoff procedure, the Tx entity may resume backoff when the        channel is sensed to be idle for an additional second interval.        In this way, the Tx entity may perform the transmission when the        channel is idle during the slot period of the backoff counter N,        in addition to the second interval. In this case, the initial        value of the backoff counter N is obtained within the CW of the        fixed size.

Category 4: LBT Performing Random Backoff by Using CW of Variable Size

-   -   The Tx entity obtains a random value within the CW of a variable        size, sets the random value to an initial value of a backoff        counter (or backoff timer) N, and performs backoff by using the        set backoff counter N. More specifically, the Tx entity may        adjust the size of the CW based on HARQ-ACK information for the        previous transmission, and the initial value of the backoff        counter N is obtained within the CW of the adjusted size. A        specific process of performing backoff by the Tx entity is as        described in Category 3. The Tx entity may perform the        transmission when the channel is idle during the slot period of        the backoff counter N, in addition to the second interval. In        this case, the initial value of the backoff counter N is        obtained within the CW of the variable size.

In the above Category 1 to Category 4, the Tx entity may be a basestation or a UE. According to an embodiment of the present invention, afirst type channel access may refer to a Category 4 channel access, anda second type channel access may refer to a Category 2 channel access.

FIG. 16 illustrates a channel access procedure based on Category 4 LBTaccording to an embodiment of the present invention.

In order to perform the channel access, first, the Tx entity performschannel sensing for the defer duration T_(d) (S302). According to anembodiment of the present invention, the channel sensing for a deferduration T_(d) in step S302 may be performed through channel sensing forat least a portion of the defer duration T_(d). For example, the channelsensing for the defer duration T_(d) may be performed through thechannel sensing during one slot period within the defer duration T_(d).The Tx entity checks whether the channel is idle through the channelsensing for the defer duration T_(d) (S304). If the channel is sensed tobe idle for the defer duration T_(d), the Tx entity proceeds to stepS306. If the channel is not sensed to be idle for the defer durationT_(d) (that is, sensed to be busy), the Tx entity returns to step S302.The Tx entity repeats steps S302 to S304 until the channel is sensed tobe idle for the defer duration T_(d). The defer duration T_(d) may beset based on the channel access priority class of the Tx entity, andconsists of a period of 16 μs and m consecutive slot periods. Here, m isa value set according to the channel access priority class.

Next, the Tx entity obtains a random value within a predetermined CW,sets the random value to the initial value of the backoff counter (orbackoff timer) N (S306), and proceeds to step S308. The initial value ofthe backoff counter N is randomly selected from values between 0 and CW.The Tx entity performs the backoff procedure by using the set backoffcounter N. That is, the Tx entity performs the backoff procedure byrepeating S308 to S316 until the value of the backoff counter N reaches0. Meanwhile, FIG. 16 illustrates that step S306 is performed after thechannel is sensed to be idle for the defer duration T_(d), but thepresent invention is not limited thereto. That is, step S306 may beperformed independently of steps S302 to S304, and may be performedprior to steps S302 to S304. When step S306 is performed prior to stepsS302 to S304, if the channel is sensed to be idle for the defer durationT_(d) by steps S302 to S304, the Tx entity proceeds to step S308.

In step S308, the Tx entity checks whether the value of the backoffcounter N is 0. If the value of the backoff counter N is 0, the Txentity proceeds to step S320 to perform a transmission. If the value ofthe backoff counter N is not 0, the Tx entity proceeds to step S310. Instep S310, the Tx entity decreases the value of the backoff counter Nby 1. According to an embodiment, the Tx entity may selectively decreasethe value of the backoff counter by 1 in the channel sensing process foreach slot. In this case, step S310 may be skipped at least once by theselection of the Tx entity. Next, the Tx entity performs channel sensingfor an additional slot period (S312). The Tx entity checks whether thechannel is idle through the channel sensing for the additional slotperiod (S314). If the channel is sensed to be idle for the additionalslot period, the Tx entity returns to step S308. In this way, the Txentity may decrease the backoff counter by 1 whenever the channel issensed to be idle for a predetermined slot period. Here, thepredetermined slot period may be 9 μs, but the present invention is notlimited thereto.

In step S314, if the channel is not sensed to be idle for the additionalslot period (that is, sensed to be busy), the Tx entity proceeds to stepS316. In step S316, the Tx entity checks whether the channel is idle forthe additional defer duration T_(d). According to an embodiment of thepresent invention, the channel sensing in step S316 may be performed inunits of slots. That is, the Tx entity checks whether the channel issensed to be idle during all slot periods of the additional deferduration T_(d). When the busy slot is detected within the additionaldefer duration T_(d), the Tx entity immediately restarts step S316. Whenthe channel is sensed to be idle during all slot periods of theadditional defer duration T_(d), the Tx entity returns to step S308.

On the other hand, if the value of the backoff counter N is 0 in thecheck of step S308, the Tx entity performs the transmission (S320). TheTx entity receives a HARQ-ACK feedback corresponding to the transmission(S322). The Tx entity may check whether the previous transmission issuccessful through the received HARQ-ACK feedback. Next, the Tx entityadjusts the CW size for the next transmission based on the receivedHARQ-ACK feedback (S324).

As described above, after the channel is sensed to be idle for the deferduration T_(d), the Tx entity may perform the transmission when thechannel is idle for N additional slot periods. As described above, theTx entity may be a base station or a UE, and the channel accessprocedure of FIG. 16 may be used for downlink transmission of the basestation and/or uplink transmission of the UE.

Hereinafter, a method for adaptively adjusting a CWS when accessing achannel in an unlicensed band is presented. The CWS may be adjustedbased on UE (User Equipment) feedback, and UE feedback used for CWSadjustment may include the HARQ-ACK feedback and CQI/PMI/RI. In thepresent invention, a method for adaptively adjusting a CWS based on theHARQ-ACK feedback is presented. The HARQ-ACK feedback includes at leastone of ACK, NACK, DTX, and NACK/DTX.

As described above, the CWS is adjusted based on ACK even in a wirelessLAN system. When the ACK feedback is received, the CWS is reset to theminimum value (CWmin), and when the ACK feedback is not received, theCWS is increased. However, in a cellular system, a CWS adjustment methodin consideration of multiple access is required.

First, for the description of the present invention, terms are definedas follows.

-   -   Set of HARQ-ACK feedback values (i.e., HARQ-ACK feedback set):        refers to HARQ-ACK feedback value(s) used for CWS        update/adjustment. The HARQ-ACK feedback set is decoded at a        time when the CWS is determined and corresponds to available        HARQ-ACK feedback values. The HARQ-ACK feedback set includes        HARQ-ACK feedback value(s) for one or more DL (channel)        transmissions (e.g., PDSCH) on an unlicensed band carrier (e.g.,        Scell, NR-U cell). The HARQ-ACK feedback set may include        HARQ-ACK feedback value(s) for a DL (channel) transmission        (e.g., PDSCH), for example, a plurality of HARQ-ACK feedback        values fed back from a plurality of UEs. The HARQ-ACK feedback        value may indicate reception response information for the code        block group (CBG) or the transport block (TB), and may indicate        any one of ACK, NACK, DTX, or NACK/DTX. Depending on the        context, the HARQ-ACK feedback value may be mixed with terms        such as a HARQ-ACK value, a HARQ-ACK information bit, and a        HARQ-ACK response.    -   Reference window: refers to a time interval in which a DL        transmission (e.g., PDSCH) corresponding to the HARQ-ACK        feedback set is performed in an unlicensed band carrier (e.g.,        Scell, NR-U cell). A reference window may be defined in units of        slots or subframes according to embodiments. The reference        window may indicate one or more specific slots (or subframes).        According to an embodiment of the present invention, the        specific slot (or reference slot) may include a start slot of        the most recent DL transmission burst in which at least some        HARQ-ACK feedback is expected to be available.

FIG. 17 illustrates an embodiment of a method of adjusting a contentionwindow size (CWS) based on HARQ-ACK feedback. In the embodiment of FIG.17, the Tx entity may be a base station and the Rx entity may be a UE,but the present invention is not limited thereto. In addition, althoughthe embodiment of FIG. 17 assumes a channel access procedure for the DLtransmission by the base station, at least some configurations may beapplied to a channel access procedure for the UL transmission by the UE.

Referring to FIG. 17, the Tx entity transmits the n-th DL transmissionburst on an unlicensed band carrier (e.g., Scell, NR-U cell) (S402), andthen if an additional DL transmission is required, the Tx entity maytransmit the (n+1)-th DL transmission burst based on the LBT channelaccess (S412). Here, the transmission burst indicates a transmissionthrough one or more adjacent slots (or subframes). FIG. 17 illustrates achannel access procedure and a CWS adjustment method based on theaforementioned first type channel access (that is, Category 4 channelaccess).

First, the Tx entity receives a HARQ-ACK feedback corresponding to thePDSCH transmission(s) on an unlicensed band carrier (e.g., Scell, NR-Ucell) (S404). The HARQ-ACK feedback used for CWS adjustment includes aHARQ-ACK feedback corresponding to the most recent DL transmission burst(that is, n-th DL transmission burst) on the unlicensed band carrier.More specifically, the HARQ-ACK feedback used for CWS adjustmentincludes a HARQ-ACK feedback corresponding to the PDSCH transmission onthe reference window within the most recent DL transmission burst. Thereference window may indicate one or more specific slots (or subframes).According to an embodiment of the present invention, the specific slot(or reference slot) includes a start slot of the most recent DLtransmission burst in which at least some HARQ-ACK feedback is expectedto be available.

When the HARQ-ACK feedback is received, a HARQ-ACK value is obtained foreach transport block (TB). The HARQ-ACK feedback includes at least oneof a TB-based HARQ-ACK bit sequence and a CBG-based HARQ-ACK. When theHARQ-ACK feedback is the TB-based HARQ-ACK bit sequence, one HARQ-ACKinformation bit is obtained per TB. On the other hand, when the HARQ-ACKfeedback is the CBG-based HARQ-ACK bit sequence, N HARQ-ACK informationbit(s) are obtained per TB. Here, N is the maximum number of CBGs per TBconfigured in the Rx entity of the PDSCH transmission. According to anembodiment of the present invention, HARQ-ACK value(s) for each TB maybe determined with the HARQ-ACK information bit(s) for each TB of theHARQ-ACK feedback for CWS determination. More specifically, when theHARQ-ACK feedback is the TB-based HARQ-ACK bit sequence, one HARQ-ACKinformation bit of the TB is determined as the HARQ-ACK value. However,when the HARQ-ACK feedback is the CBG-based HARQ-ACK bit sequence, oneHARQ-ACK value may be determined based on N HARQ-ACK information bit(s)corresponding to CBGs included in the TB.

Next, the Tx entity adjusts the CWS based on the HARQ-ACK valuesdetermined in step S404 (S406). That is, the Tx entity determines theCWS based on the HARQ-ACK value(s) determined with the HARQ-ACKinformation bit(s) for each TB of the HARQ-ACK feedback. Morespecifically, the CWS may be adjusted based on the ratio of NACKs amongHARQ-ACK value(s). First, variables may be defined as follows.

-   -   p: Priority class value    -   CW_min_p: Predetermined CWS minimum value of priority class p    -   CW_max_p: Predetermined CWS maximum value of priority class p    -   CW_p: CWS for transmission of priority class p. CW_p is set to        any one of a plurality of CWS values between CW_min_p and        CW_max_p included in the allowed CWS set of the priority class        p.

According to an embodiment of the present invention, the CWS may bedetermined according to the following steps.

Step A-1) For every priority class p, CW_p is set to CW_min_p. In thiscase, the priority class p includes {1, 2, 3, 4}.

Step A-2) When the ratio of NACKs to HARQ-ACK values for the PDSCHtransmission(s) of the reference window k is Z % or more, CW_p isincreased to the next highest allowed value for every priority class p(further, Step A-2 remains). Otherwise, Step A proceeds to Step A-1.Here, Z is a predetermined integer in the range of 0<=Z<=100, andaccording to an embodiment, it may be set to one of {30, 50, 70, 80,100}.

Here, the reference window k includes the start slot (or subframe) ofthe most recent transmission by the Tx entity. In addition, thereference window k is a slot (or subframe) in which at least some of theHARQ-ACK feedbacks is expected to be possible. If CW_p=CW_max_p, thenext highest allowed value for CW_p adjustment is CW_max_p.

Next, the Tx entity selects a random value within the CWS determined instep S406 and sets the random value to the initial value of the backoffcounter N (S408). The Tx entity performs backoff by using the setbackoff counter N (S410). That is, the Tx entity may decrease thebackoff counter by 1 for each slot period in which the channel is sensedto be idle. When the value of the backoff counter reaches 0, the Txentity may transmit the (n+1)-th DL transmission burst in the channel(S412).

Meanwhile, in the above-described CWS adjustment process, determinationhas to be made as to whether not only ACK and NACK but also DTX orNACK/DTX are considered together among HARQ-ACK feedbacks. According toan embodiment of the present invention, depending on whether thetransmission in the unlicensed band is based on self-carrier schedulingor cross-carrier scheduling, determination may be made as to whether DTXor NACK/DTX is considered together in the CWS adjustment process.

In self-carrier scheduling, a DL transmission (e.g., PDSCH) on theunlicensed band carrier is scheduled through the control channel (e.g.,(E)PDCCH) transmitted on the same unlicensed band carrier. Here, sincethe DTX indicates a failure of the DL transmission by a hidden node orthe like in the unlicensed band carrier, it may be used for CWSadjustment together with NACK. In addition, DTX is one of the methods inwhich the UE informs the base station that the UE fails to decode thecontrol channel even though the base station transmits, to the UE, thecontrol channel including scheduling information (e.g., (E)PDCCH). DTXmay be determined only by the HARQ-ACK feedback value, or may bedetermined taking into account the HARQ-ACK feedback value and theactual scheduling situation. According to an embodiment of the presentinvention, DTX and NACK/DTX may be counted as NACK for CWS adjustment inthe self-carrier scheduling situation. That is, when the ratio of thesum of NACK, DTX, and NACK/DTX to HARQ-ACK values for the PDSCHtransmission(s) of the reference window k is equal to or greater than Z%, the CWS is increased to the next highest allowed value. Otherwise,the CWS is reset to the minimum value.

In cross-carrier scheduling, a DL transmission (e.g., PDSCH) on theunlicensed band carrier may be scheduled through the control channel(e.g., (E)PDCCH) transmitted on the licensed band carrier. In this case,since the DTX feedback is used to determine the decoding situation ofthe UE for the control channel transmitted on the licensed band carrier,it is not helpful to adaptively adjust the CWS for a channel access inthe unlicensed band. Therefore, according to an embodiment of thepresent invention, DTX may be ignored for CWS determination in thecross-carrier scheduling situation from the licensed band. That is, forCWS adjustment, among HARQ-ACK value(s), only ACK and NACK may beconsidered for calculating the ratio of NACK, or only ACK, NACK andNACK/DTX may be considered for calculating the ratio of NACK. Therefore,when calculating the ratio of the NACK, DTX may be excluded.

FIG. 18 is a block diagram showing the configurations of a UE and a basestation according to an embodiment of the present invention. In anembodiment of the present invention, the UE may be implemented withvarious types of wireless communication devices or computing devicesthat are guaranteed to be portable and mobile. The UE may be referred toas a User Equipment (UE), a Station (STA), a Mobile Subscriber (MS), orthe like. In addition, in an embodiment of the present invention, thebase station controls and manages a cell (e.g., a macro cell, a femtocell, a pico cell, etc.) corresponding to a service area, and performsfunctions of a signal transmission, a channel designation, a channelmonitoring, a self diagnosis, a relay, or the like. The base station maybe referred to as next Generation NodeB (gNB) or Access Point (AP).

As shown in the drawing, a UE 100 according to an embodiment of thepresent disclosure may include a processor 110, a communication module120, a memory 130, a user interface 140, and a display unit 150.

First, the processor 110 may execute various instructions or programsand process data within the UE 100. In addition, the processor 100 maycontrol the entire operation including each unit of the UE 100, and maycontrol the transmission/reception of data between the units. Here, theprocessor 110 may be configured to perform an operation according to theembodiments described in the present invention. For example, theprocessor 110 may receive slot configuration information, determine aslot configuration based on the slot configuration information, andperform communication according to the determined slot configuration.

Next, the communication module 120 may be an integrated module thatperforms wireless communication using a wireless communication networkand a wireless LAN access using a wireless LAN. For this, thecommunication module 120 may include a plurality of network interfacecards (NICs) such as cellular communication interface cards 121 and 122and an unlicensed band communication interface card 123 in an internalor external form. In the drawing, the communication module 120 is shownas an integral integration module, but unlike the drawing, each networkinterface card can be independently arranged according to a circuitconfiguration or usage.

The cellular communication interface card 121 may transmit or receive aradio signal with at least one of the base station 200, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in a first frequency band based on theinstructions from the processor 110. According to an embodiment, thecellular communication interface card 121 may include at least one NICmodule using a frequency band of less than 6 GHz. At least one NICmodule of the cellular communication interface card 121 mayindependently perform cellular communication with at least one of thebase station 200, an external device, and a server in accordance withcellular communication standards or protocols in the frequency bandsbelow 6 GHz supported by the corresponding NIC module.

The cellular communication interface card 122 may transmit or receive aradio signal with at least one of the base station 200, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in a second frequency band based on theinstructions from the processor 110. According to an embodiment, thecellular communication interface card 122 may include at least one NICmodule using a frequency band of more than 6 GHz. At least one NICmodule of the cellular communication interface card 122 mayindependently perform cellular communication with at least one of thebase station 200, an external device, and a server in accordance withcellular communication standards or protocols in the frequency bands of6 GHz or more supported by the corresponding NIC module.

The unlicensed band communication interface card 123 transmits orreceives a radio signal with at least one of the base station 200, anexternal device, and a server by using a third frequency band which isan unlicensed band, and provides an unlicensed band communicationservice based on the instructions from the processor 110. The unlicensedband communication interface card 123 may include at least one NICmodule using an unlicensed band. For example, the unlicensed band may bea band of 2.4 GHz, 5 GHz, 6 GHz, 7 GHz or above 52.6 GHz. At least oneNIC module of the unlicensed band communication interface card 123 mayindependently or dependently perform wireless communication with atleast one of the base station 200, an external device, and a serveraccording to the unlicensed band communication standard or protocol ofthe frequency band supported by the corresponding NIC module.

The memory 130 stores a control program used in the UE 100 and variouskinds of data therefor. Such a control program may include a prescribedprogram required for performing wireless communication with at least oneamong the base station 200, an external device, and a server.

Next, the user interface 140 includes various kinds of input/outputmeans provided in the UE 100. In other words, the user interface 140 mayreceive a user input using various input means, and the processor 110may control the UE 100 based on the received user input. In addition,the user interface 140 may perform an output based on instructions fromthe processor 110 using various kinds of output means.

Next, the display unit 150 outputs various images on a display screen.The display unit 150 may output various display objects such as contentexecuted by the processor 110 or a user interface based on controlinstructions from the processor 110.

In addition, the base station 200 according to an embodiment of thepresent invention may include a processor 210, a communication module220, and a memory 230.

First, the processor 210 may execute various instructions or programs,and process internal data of the base station 200. In addition, theprocessor 210 may control the entire operations of units in the basestation 200, and control data transmission and reception between theunits. Here, the processor 210 may be configured to perform operationsaccording to embodiments described in the present invention. Forexample, the processor 210 may signal slot configuration and performcommunication according to the signaled slot configuration.

Next, the communication module 220 may be an integrated module thatperforms wireless communication using a wireless communication networkand a wireless LAN access using a wireless LAN. For this, thecommunication module 220 may include a plurality of network interfacecards such as cellular communication interface cards 221 and 222 and anunlicensed band communication interface card 223 in an internal orexternal form. In the drawing, the communication module 220 is shown asan integral integration module, but unlike the drawing, each networkinterface card can be independently arranged according to a circuitconfiguration or usage.

The cellular communication interface card 221 may transmit or receive aradio signal with at least one of the base station 100, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in the first frequency band based onthe instructions from the processor 210. According to an embodiment, thecellular communication interface card 221 may include at least one NICmodule using a frequency band of less than 6 GHz. The at least one NICmodule of the cellular communication interface card 221 mayindependently perform cellular communication with at least one of thebase station 100, an external device, and a server in accordance withthe cellular communication standards or protocols in the frequency bandsless than 6 GHz supported by the corresponding NIC module.

The cellular communication interface card 222 may transmit or receive aradio signal with at least one of the base station 100, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in the second frequency band based onthe instructions from the processor 210. According to an embodiment, thecellular communication interface card 222 may include at least one NICmodule using a frequency band of 6 GHz or more. The at least one NICmodule of the cellular communication interface card 222 mayindependently perform cellular communication with at least one of thebase station 100, an external device, and a server in accordance withthe cellular communication standards or protocols in the frequency bands6 GHz or more supported by the corresponding NIC module.

The unlicensed band communication interface card 223 transmits orreceives a radio signal with at least one of the base station 100, anexternal device, and a server by using the third frequency band which isan unlicensed band, and provides an unlicensed band communicationservice based on the instructions from the processor 210. The unlicensedband communication interface card 223 may include at least one NICmodule using an unlicensed band. For example, the unlicensed band may bea band of 2.4 GHz, 5 GHz, 6 GHz, 7 GHz or above 52.6 GHz. At least oneNIC module of the unlicensed band communication interface card 223 mayindependently or dependently perform wireless communication with atleast one of the base station 100, an external device, and a serveraccording to the unlicensed band communication standards or protocols ofthe frequency band supported by the corresponding NIC module.

FIG. 18 is a block diagram illustrating the UE 100 and the base station200 according to an embodiment of the present invention, and blocksseparately shown are logically divided elements of a device.Accordingly, the aforementioned elements of the device may be mounted ina single chip or a plurality of chips according to the design of thedevice. In addition, a part of the configuration of the UE 100, forexample, a user interface 140, a display unit 150 and the like may beselectively provided in the UE 100. In addition, the user interface 140,the display unit 150 and the like may be additionally provided in thebase station 200, if necessary.

A channel access procedure performed by a wireless communication deviceaccording to an embodiment of the present invention in an unlicensedband will be described with reference to FIG. 19. Specifically, an LBTprocedure used when a wireless communication device according to anembodiment of the present invention performs a channel access in anunlicensed band will be described. In particular, a channel access inwhich the wireless communication device performs a transmissionaccording to a result of channel sensing within a time interval of apredetermined duration may be configured in the wireless communicationdevice. In this case, a method for operating a wireless communicationdevice when the wireless communication device fails to access a channelwill be described. The specified duration which has been mentionedearlier may be 16 μs.

For convenience of description, the wireless communication device, whichis a wireless endpoint that initiates channel occupation, is referred toas an initiating node. In addition, a wireless communication device,which is a wireless endpoint communicating with the initiating node, isreferred to as a responding node. The initiating node may be a basestation and the responding node may be a UE. In addition, the initiatingnode may be a UE and the responding node may be a base station. When theinitiating node intends to transmit data, the initiating node mayperform a channel access according to a channel access priority classdetermined according to the type of data. In this case, a parameter usedfor a channel access may be determined according to the type of data.The parameters used for the channel access may include any one of theminimum value of the CW, the maximum value of the CW, the maximumoccupancy time (MCOT), which is the maximum duration capable ofoccupying a channel in one channel occupancy, and the number (m_(p)) ofsensing slots. Specifically, the initiating node may perform theabove-described Category 4 LBT according to the channel access priorityclass determined according to the type of data.

Table 4 below shows an example of values of parameters used for achannel access according to the channel access priority class.Specifically, Table 4 shows values of parameters used for a channelaccess for each channel access priority class for the downlinktransmission in the LTE LAA system.

When the downlink channel transmitted by the wireless communicationdevice includes data traffic, the defer duration may be configuredaccording to the channel access priority class of traffic included inthe downlink channel. In addition, the defer duration may include aninitial duration T_(f) or one or more (m_(p)) slot durations T_(sl). Inthis case, the slot duration T_(sl) may be 9 μs. The initial durationincludes one idle slot duration T_(sl). In addition, the number (m_(p))of slot durations included in the defer duration may be configuredaccording to the above-described channel access priority class.Specifically, the number (m_(p)) of slot durations included in the deferduration may be configured as shown in Table 4.

TABLE 4 Channel Access Priority Class allowed (p) m_(p) CW_(min, p)CW_(max, p) T_(mcot, p) CW_(p) sizes 1 1 3 7 2 ms {3, 7}  2 1 7 15 3 ms{7, 15} 3 3 15 63 8 or 10 ms {15, 31, 63} 4 7 15 1023 8 or 10 ms {15,31, 63, 127, 255, 511, 1023}

In addition, the wireless communication device may configure the rangeof the CW values according to the channel access priority class.Specifically, the wireless communication device may set the value of theCW to satisfy CW_(min,p)<=CW<=CW_(max,p). In this case, the minimumvalue CW_(min,p) and the maximum value CW_(max,p) of the CW may bedetermined according to the channel access priority class. Specifically,the minimum value CW_(min,p) and the maximum value CW_(max,p) of the CWmay be determined as shown in Table 4. The wireless communication devicemay set a minimum value CW_(min,p) and a maximum value CW_(max,p) of CWin a counter value setting procedure. When the wireless communicationdevice accesses the channel, the wireless communication device mayadjust the value of the CW as described above with reference to FIGS. 15to 17. In addition, in the wireless communication device of theunlicensed band, the MCOT T_(mcot,p) may be determined according to thechannel access priority of data included in the transmission asdescribed above. Specifically, the MCOT may be determined as shown inTable 4. Accordingly, the wireless communication device may not beallowed to perform continuous transmissions for a time exceeding theMCOT in the unlicensed band. This is because the unlicensed band is afrequency band used by various wireless communication devices accordingto certain rules. In Table 4, when the value of the channel accesspriority class is p=3 or p=4, the unlicensed band is used for a longterm according to the regulations, and there is no wirelesscommunication device using other technology, the wireless communicationdevice may be configured with T_(mcot,p)=10 ms. Otherwise, the wirelesscommunication device may be configured with T_(mcot,p)=8 ms.

Table 5 shows values of parameters used for a channel access for eachchannel access priority class for uplink transmission used in the LTELAA system.

TABLE 5 LBT priority Set of class n CWmin CWmax MCOT CW sizes 1 2 3 7 2ms {3, 7}  2 2 7 15 4 ms {7, 15} 3 3 15 1023 6 ms (see note 1) or {15,31, 10 ms (see note 2) 63, 127, 255, 511, 1023} 4 7 15 1023 6 ms (seenote 1) or {15, 31, 10 ms (see note 2) 63, 127, 255, 511, 1023} NOTE 1:The MCOT of 6 ms may be increased to 8 ms by inserting one or more gaps.The minimum duration of a pause shall be 100 μs. The maximum duration(Channel Occupancy) before including any such gap shall be 6 ms. The gapduration is not included in the channel occupancy time. NOTE 2: If theabsence of any other technology sharing the carrier can be guaranteed ona long term basis (e.g. by level of regulation), the maximum channeloccupancy time (MCOT) for LBT priority classes 3 and 4 is for 10 ms,otherwise, the MCOT for LBT priority classes 3 and 4 is 6 ms as in note1.

As described in Table 5, the MCOT value 6 ms may be increased to 8 mswhen one or more gaps are included in the transmission. The gaprepresents the time from when the transmission is stopped in a carrieruntil the transmission is resumed in the carrier. In this case, theminimum value of the duration of the gap is 100 μs. Furthermore, themaximum value of the duration of transmission performed before the gapis included is 6 ms. Furthermore, the duration of the gap is notincluded in the channel occupancy time. When the value of the channelaccess priority class is 3 or 4 and it is guaranteed that no other radioaccess technology is used in the carrier on which the channel access isperformed, the value of MCOT may be 10 ms. In this case, anotherwireless access technology may include Wi-Fi. Otherwise, the value ofthe MCOT may be determined as described in Note 1 of Table 5.

The COT represents the time the wireless communication device occupies achannel. As described above, the MCOT represents a time during which theinitiating node is able to continuously occupy a channel in any onecarrier of a unlicensed band to the maximum. However, as describedabove, the gap, which is an interval in which the transmission is notperformed, may be included between a plurality of transmissions, andwhen the gap is included, the value of the MCOT may be applieddifferently.

FIG. 19 illustrates that when the duration of transmission of aninitiating node within a channel occupancy initiated by the initiatingnode does not exceed an MCOT of the channel occupancy, a responding nodeperforms a transmission within the channel occupancy initiated by theinitiating node, according to an embodiment of the present invention.That is, FIG. 19 illustrates that after the initiating node completes atransmission in any one channel, the responding node performs thetransmission in the channel. As described above, it may be described assharing the channel occupancy that the initiating node and theresponding node perform transmissions in one channel.

If the duration of transmission of the initiating node is less than theduration of the MCOT, the responding node may perform the transmissionwithin the channel occupancy initiated by the initiating node. FIG. 19shows such a case, where a gap between the transmission of theinitiating node and the transmission of the responding node is 16 μs. Inthis case, a method for performing a channel access by the respondingnode may be problematic.

In an embodiment of the present invention, when the duration of the gapis not greater than the first duration, the responding node may performa transmission immediately after the gap without sensing. Specifically,the responding node may perform the above-described Category 1 channelaccess. The first duration may be 16 μs, and this may be applied toembodiments to be described later. In the embodiment, additionalconstrains other than the MCOT may be applied to the duration oftransmission of the responding node. In a specific embodiment, theresponding node may perform the transmission within a predeterminedduration. In this case, the predetermined duration may be a constraintapplied to the transmission of the responding node separately from theMCOT. Specifically, the predetermined duration may be 584 μs.

In an embodiment of the present invention, when the duration of the gapis the same as the first duration, the responding node may perform thefirst fixed duration-based channel access for the transmission followingthe gap. The first fixed duration-based channel access is a channelaccess in which, when the channel is sensed to be idle within the firstfixed duration, the wireless communication device performing the firstfixed duration-based channel access is allowed to perform a transmissionimmediately after the first fixed duration. Specifically, in the firstfixed duration-based channel access, the wireless communication deviceperforms channel sensing within the first fixed duration and performs atransmission on the channel when the channel is sensed to be idle withinthe fixed duration. The first fixed duration-based channel access may bethe above-described Category 2 LBT. In the embodiment, the initiatingnode may implicitly or explicitly indicate the first fixedduration-based channel access to the responding node. For example, thebase station, which is the initiating node, may indicate the first fixedduration-based channel access to the responding node by using a grant.

In an embodiment of the present invention, when the gap betweenconsecutively scheduled or granted transmissions within the channeloccupancy initiated by the initiating node is not greater than thesecond fixed duration, the node performing the second transmission mayperform the second fixed duration-based channel access. The second fixedduration-based channel access is a channel access in which, when thechannel is idle while having the second fixed duration, the wirelesscommunication device performing the second fixed duration-based channelaccess is allowed to perform a transmission immediately after the secondfixed duration. Specifically, in the second fixed duration-based channelaccess, the wireless communication device performs channel sensing forthe second fixed duration and performs a transmission on the channelwhen the channel is sensed to be idle for the fixed duration. The secondfixed duration may be greater than the first fixed duration describedabove. Specifically, the second duration may be 25 μs, and this may beapplied to embodiments to be described later. In addition, even when theuplink transmission is not followed by the downlink transmission withinthe same channel occupancy, the UE may perform the second fixedduration-based channel access for the uplink transmission after theuplink transmission. In addition, even when the downlink transmission isnot followed by the uplink transmission within the same channeloccupancy, the UE may perform the second fixed duration-based channelaccess for the uplink transmission. In addition, when the gap betweenthe uplink transmission and the subsequent downlink transmission isgreater than 16 μs and not greater than 25 μs within the same channeloccupancy, the base station may perform the second fixed duration-basedchannel access for the downlink transmission.

Embodiments applied when the gap is not greater than the first fixedduration will be described. In this case, the first fixed duration maybe 16 μs as described above.

When the gap is not greater than the first fixed duration, theresponding node performing the transmission following the gap mayimmediately perform a transmission without sensing or may perform thetransmission by performing the first fixed duration-based channelaccess. In this case, the responding node may immediately perform thetransmission without sensing or may perform the transmission byperforming the first fixed duration-based channel access, depending onwhether the transmission following the gap includes data traffic thatmay be classified as traffic or data traffic that determines the channelaccess priority class. Specifically, when the responding node transmitsa HARQ-ACK feedback for data traffic transmitted from the initiatingnode, the responding node may immediately perform the transmissionwithout sensing.

In another specific embodiment, when the responding node transmitsuplink control information (UCI) for data traffic transmitted from theinitiating node, the responding node may immediately perform thetransmission without sensing.

In another specific embodiment, when the responding node transmits theSRS, the responding node may immediately perform the transmissionwithout sensing.

In another specific embodiment, when the responding node transmits aphysical random access channel (PRACH), the responding node mayimmediately perform the transmission without sensing.

In the above-described embodiments, when the responding node performsthe transmission including data traffic immediately after the gap, theresponding node may perform the first fixed duration-based channelaccess. Specifically, when data traffic is scheduled or configured bythe initiating node, the responding node may perform the first fixedduration-based channel access. When it is possible to classify the datatraffic as traffic or determine the channel access priority class of thedata traffic, the responding node may perform the first fixedduration-based channel access.

In the above-described embodiments, the responding node's immediatelyperforming the transmission without sensing may represent that theinitiating node performs the above-described Category 4 channel access.As described above, the first fixed duration-based channel access may bethe Category 2 LBT.

In the COT initiated by the initiating node, the initiating node mayperform the transmission following the transmission of the respondingnode. In this case, in the COT initiated by the initiating node, the gapbetween the transmission of the initiating node and the subsequenttransmission of the responding node may not be greater than the firstfixed duration. The initiating node may immediately perform thetransmission without sensing or may perform the transmission byperforming the first fixed duration-based channel access, depending onwhether the transmission after the gap includes data traffic that may beclassified as traffic or data traffic that determines the channel accesspriority class.

Specifically, when the initiating node transmits only controlinformation for scheduling data transmitted by the responding node, theinitiating node may immediately perform the transmission withoutsensing. In this case, the control information may be at least one ofPDCCH only, group common signaling, paging, a reference signal only, atracking reference signal (TRS), a RACH message 4, or a handovercommand.

In yet another specific embodiment, when the initiating node transmitsonly broadcasting information, the initiating node may immediatelyperform the transmission without sensing. In this case, the broadcastinginformation may be at least one of a discovery reference signal (DRS),an SS/PBCH block, a Type0-PDCCH, or remaining system information (RMSI).

In the above-described embodiments, when the initiating node performsthe transmission including data traffic immediately after the gap, theinitiating node may perform the first fixed duration-based channelaccess. Specifically, when the data traffic schedules the respondingnode or is configured for the responding node, the initiating node mayperform the first fixed duration-based channel access. When the datatraffic is classified as traffic or the data traffic determines thechannel access priority class, the initiating node may perform the firstfixed duration-based channel access.

In the above-described embodiments, the initiating node's immediatelyperforming the transmission without sensing may represent that theinitiating node performs the aforementioned Category 4 channel access.As described above, the first fixed duration-based channel access may bethe Category 2 LBT.

In the above-described embodiments, the initiating node may be a basestation and the responding node may be a UE. That is, in theabove-described embodiments, the channel occupancy may be initiated by abase station. In addition, the initiating node may be a UE and theresponding node may be a base station. That is, in the above-describedembodiments, the channel occupancy may be initiated by a UE.

In the above-described embodiments, a node performing the transmissionafter the gap may perform the transmission within the MCOT.

FIG. 20 illustrates an operation of a UE when a downlink transmissiondoes not occupy as much as a MCOT within a COT initiated by a basestation and transmission of the UE is scheduled or configured by thebase station, according to an embodiment of the present invention.

In FIG. 20, a gap between the downlink transmission of the base stationand the uplink transmission of the UE is 16 μs. In the case of FIG.20(a), the downlink transmission includes a plurality of UL grants forscheduling a PUSCH transmission in units of slots. The UE transmitsPUSCHs in a plurality of slots based on a plurality of UL grants. In thecase of FIG. 20(b), the downlink transmission includes one UL grant forscheduling the PUSCH transmission in a plurality of slots. The UEtransmits the PUSCH in a plurality of slots based on the UL grant. InFIG. 20, scheduling for uplink transmission is performed within thechannel occupancy acquired by the base station, which is an initiatingnode, but configuration or scheduling of uplink transmission may beperformed before the channel occupancy. Even in this case, embodimentsto be described later may be applied.

The initiating node may be a base station and the responding node may bea UE. When the gap between the transmission of the initiating node andthe transmission of the responding node is the first fixed duration, thebase station may implicitly or explicitly indicate the first fixedduration-based channel access. For example, the base station, which isthe initiating node, may indicate the first fixed duration-based channelaccess to the responding node by using the UL grant. In this case, theUE senses the channel within the first fixed duration. When the channelis sensed to be idle during the first duration, the UE immediatelyperforms the transmission after the first fixed duration. When thechannel is sensed to be busy during the first duration, a method foroperating the UE is problematic. Specifically, as described above, theuplink transmission of the UE on a plurality of slots may be scheduledor configured. In this case, even if the UE fails to access the channelin the first slot among the plurality of slots, a channel access for theuplink transmission may be required in a slot other than the first slotamong the plurality of slots. In this case, the method for operating theUE will be described. For convenience of description, a plurality ofslots in which uplink transmission of the UE is scheduled or configureddenoted by {slot(n), slot(n+1), slot(n+2), . . . , slot(n+k−1)}, and thenumber of a plurality of slots is denoted by k.

For the UE, a plurality of uplink transmissions may be scheduled orconfigured. A plurality of uplink transmissions may be continuouswithout a gap. Specifically, the UE may receive a grant for scheduling aplurality of uplink transmissions from the base station. The grantrefers to downlink control information (DCI), and may include a DL grantor a UL grant for scheduling uplink transmissions. In the specificembodiment, the DL grant or the UL grant may indicate a fixedduration-based channel access as a channel access type, and may indicatea channel access priority used to access a channel in which theplurality of uplink transmissions are performed. In this case, the DLgrant or the UL grant may indicate the first fixed duration-basedchannel access as the channel access type.

The UE may attempt the first fixed duration-based channel access for thefirst transmission which is one of the plurality of uplinktransmissions, and the UE may attempt the first fixed duration-basedchannel access for a second transmission which is a transmissionfollowing the first transmission when the first fixed duration-basedchannel access fails. When the UE succeeds in the first fixedduration-based channel access, the UE may perform the secondtransmission. In a specific embodiment, the UE may perform the firstfixed duration-based channel access for uplink transmission for each ofthe remaining slots slot(n+1), slot(n+2), . . . , slot(n+k−1) after thefirst slot slot(n) of a plurality of slots.

In another specific embodiment, the UE may perform the first fixedduration-based channel access for uplink transmission a predeterminednumber of times in the remaining slots slot(n+1), slot(n+2), . . . ,slot(n+k−1) after the first slot slot(n) of the plurality of slots. Inthis case, the predetermined number of times may be limited to k−1.

In yet another specific embodiment, the UE may attempt the first fixedduration-based channel access for the first transmission which is one ofthe plurality of uplink transmissions, and the UE may attempt the firstfixed duration-based channel access or a random backoff-based accessdepending on whether the channel is continuously sensed to be idle for asecond transmission which is a transmission following the firsttransmission when the first fixed duration-based channel access fails.When the UE fails in the first fixed duration-based channel access inthe first slot slot(n) and the channel is continuously sensed to be idleafter the failure of the channel access by the UE, the UE may attemptthe first fixed duration-based channel access for the secondtransmission. In this case, when the UE succeeds in the first fixedduration-based channel access, the UE may perform the secondtransmission. In addition, when the UE fails in the first fixedduration-based channel access in the first slot slot(n) and the channelis not continuously sensed to be idle after the failure of the channelaccess by the UE, the UE may perform a random backoff-based channelaccess for the uplink transmission, in the remaining slots slot(n+1),slot(n+2), . . . , slot(n+k−1) after the first slot slot(n) of theplurality of slots. When the UE succeeds in the random backoff-basedchannel access, the UE may perform the second transmission. In thiscase, when the random backoff-based channel access as a channel accessmethod is indicated to the UE through DCI in the first slot slot(n) orremaining slots slot(n+1), . . . , slot(n+2), . . . , slot(n+k−1) afterthe first slot slot(n), of the plurality of slots, the UE may performthe random backoff-based channel access by using the channel accesspriority class indicated by the DCI. When other channel access methods,other than the random backoff-based channel access, as a channel accessmethod are indicated to the UE through DCI in all of the plurality ofslots slot(n), slot(n+1), slot(n+2), . . . , slot(n+k−1), the UE mayperform the random backoff-based channel access for uplink transmissionby using the channel access priority class indicated through thescheduling DCI. To this end, when the base station indicates the fixedduration-based channel access in the DCI, the base station may indicatethe channel access priority class used to obtain access to the channelin the DCI. Specifically, when the base station indicates the firstfixed duration-based channel access in the DCI, the base station mayindicate the channel access priority class used to obtain access to thechannel in the DCI.

In yet another specific embodiment, the UE may attempt the first fixedduration-based channel access for the first transmission which is one ofthe plurality of uplink transmissions, and the UE may attempt the secondfixed duration-based channel access for the second transmission which isa transmission following the first transmission when the first fixedduration-based channel access fails. When the UE succeeds in the secondfixed duration-based channel access, the UE may perform the secondtransmission. Specifically, after the UE fails in the first fixedduration-based channel access in the first slot slot(n), the UE maysense whether or not the UE is idle every sensing slot T_(sl). When theUE fails in the first fixed duration-based channel access in the firstslot slot(n) and the channel is continuously sensed to be idle after thefailure of the channel access by the UE, the UE may perform the secondfixed duration-based channel access for uplink transmission, in theremaining slots slot(n+1), slot(n+2), . . . , slot(n+k−1) after thefirst slot slot(n) of the plurality of slots. This is performed bytaking it into account that the first fixed duration-based channelaccess may be performed when the gap is the first fixed duration period,and the channel access fails in the first slot slot(n) and thus the gapbetween transmissions is increased. When the UE fails in the first fixedduration-based channel access in the first slot slot(n) and the channelis not continuously sensed to be idle after the failure of the channelaccess by the UE, the UE may perform the random backoff-based channelaccess for uplink transmission, in the remaining slots slot(n+1),slot(n+2), . . . , slot(n+k−1) after the first slot slot(n) of theplurality of slots. When the UE succeeds in the random backoff-basedchannel access, the UE may perform the second transmission. In thiscase, when the random backoff-based channel access as a channel accessmethod is indicated to the UE through DCI in the first slot slot(n) orremaining slots slot(n+1), slot(n+2), . . . , slot(n+k−1) after thefirst slot slot(n), of the plurality of slots, the UE may perform therandom backoff-based channel access by using the channel access priorityclass indicated by the DCI. When other channel access methods, otherthan the random backoff-based channel access, as a channel access methodare indicated to the UE through DCI in all of the plurality of slotsslot(n), slot(n+1), slot(n+2), . . . , slot(n+k−1), the UE may performthe random backoff-based channel access for uplink transmission by usingthe channel access priority class indicated through the scheduling DCI.To this end, when the base station indicates the fixed duration-basedchannel access in the DCI, the base station may indicate the channelaccess priority class used to obtain access to the channel in the DCI.Specifically, when the base station indicates the first fixedduration-based channel access in the DCI, the base station may indicatethe channel access priority class used to obtain access to the channelin the DCI.

In yet another specific embodiment, a gap of the first fixed durationmay be configured between the transmission from the base station and theuplink transmission that the UE intends to transmit, and thus the UE mayswitch the channel access type to the first fixed duration-based channelaccess for the first transmission which is one of the plurality ofuplink transmissions. In this case, when the first fixed duration-basedchannel access fails, the UE may attempt a channel access according tothe channel access type indicated through DCI for the secondtransmission, which is a transmission following the first transmission.When the UE succeeds in the channel access, the UE may perform thesecond transmission. Specifically, when the UE fails in the first fixedduration-based channel access in the first slot slot(n), the UE mayperform the channel access for uplink transmission according to thechannel access type indicated through the DCI, in the remaining slotsslot(n+1), slot(n+2), . . . , slot(n+k−1) after the first slot slot(n)of the plurality of slots. In addition, when a plurality of grantsschedule uplink transmissions on a plurality of slots, the channelaccess type for uplink transmission may be indicated for each slot. TheUE may perform the channel access for uplink transmission according tothe channel access type indicated for each of the remaining slotsslot(n+1), slot(n+2), . . . , slot(n+k−1) after the first slot slot(n)of the plurality of slots. In the embodiment, when the channel accesstype indicated through DCI is the first fixed duration-based channelaccess, the operation of the UE may be the same as the first and secondembodiments described. However, when the channel access type indicatedthrough DCI is not the first fixed duration-based channel access, theoperation of the UE differs from the first and second embodimentsdescribed.

In yet another specific embodiment, when the UE fails in the first fixedduration-based channel access in the first slot slot(n), the UE mayperform the random backoff-based channel access for uplink transmissionin the remaining slots slot(n+1), slot(n+2), . . . , slot(n+k−1) afterthe first slot slot(n) of the plurality of slots. This takes intoaccount the possibility that the channel is not idle and that thechannel is being busy due to other nodes using unlicensed band.Specifically, in the embodiment, when the channel is sensed to be busyrather than idle through the first fixed duration-based channel access,even if the first fixed duration-based channel access or the secondfixed duration-based channel access is continuously performed, thechannel is being busy due to other nodes, and thus it is highly likelythat the channel is not idle and is busy. Therefore, this is a method inwhich the UE performs uplink transmission after performing the randombackoff-based channel access for transmission for the slot(n+1) andsubsequent slot.

In the above-described embodiments, the random backoff-based channelaccess may be Category 4 LBT.

Regarding the case where uplink transmissions are scheduled, previousembodiments of the present invention have been described with a focus onthe case where uplink transmissions are scheduled by the schedulinggrant. The above-described embodiments may be applied even whenresources in units of time and frequency are configured by the RRCconfiguration, and the UE performs uplink transmission in the configuredresource.

Although the method and system of the present invention have beendescribed in connection with specific embodiments, some or all ofcomponents or operations thereof may be implemented using a computingsystem having a general-purpose hardware architecture.

The description of the present invention described above is onlyexemplary, and it will be understood by those skilled in the art towhich the present invention pertains that various modifications andchanges can be made without changing the technical spirit or essentialfeatures of the present invention. Therefore, it should be construedthat the embodiments described above are illustrative and notrestrictive in all respects. For example, each component described as asingle type may be implemented in a distributed manner, and similarly,components described as being distributed may also be implemented in acombined form.

The scope of the present invention is indicated by the attached claimsrather than the detailed description, and it should be construed thatall changes or modifications derived from the meaning and scope of theclaims and their equivalents are included in the scope of the presentinvention.

1-20. (canceled)
 21. A user equipment (UE) for use in a 3^(rd)generation partnership project new radio (3GPP NR)-based wirelesscommunication system supporting operations in an unlicensed band, the UEcomprising: a communication module; and a processor controlling thecommunication module, wherein the processor is configured to: receive atleast one uplink (UL) grant for scheduling a plurality of consecutive ULtransmissions on the unlicensed band, wherein the at least one UL grantindicates a channel access type as one of at least: a first channelaccess type based on a back-off, and a second channel access type basedon a fixed sensing duration only, the fixed sensing duration including16 us and 25 us; based on the indicated channel access type, attempt afirst channel access to perform an UL transmission, which is not a lastUL transmission, among the plurality of consecutive UL transmissions onthe unlicensed band; and based on (1) the first channel accesscorresponding to the second channel access type with a fixed sensingduration of 16 us, and (2) the first channel access being failed,attempt a second channel access to perform a next UL transmission amongthe plurality of consecutive UL transmissions, according to the secondchannel access type with a fixed sensing duration of 25 us.
 22. The UEof claim 21, wherein, based on (1) and (2) being satisfied, the secondchannel access is attempted according to the second channel access typewith the fixed sensing duration of 25 us, regardless of the indicatedchannel access type.
 23. The UE of claim 21, wherein the at least one ULgrant is received via at least one physical downlink control channel(PDCCH), and the plurality of consecutive UL transmissions includes aplurality of consecutive physical uplink shared channel (PUSCH)transmissions.
 24. The UE of claim 21, wherein the plurality ofconsecutive UL transmissions is within a channel occupancy time (COT)initiated based on a downlink (DL) transmission.
 25. The UE of claim 21,wherein the UL grant further indicates a channel access priorityassociated with the indicated channel access type.
 26. The UE of claim21, wherein the at least UL grant includes a single UL grant, and thesingle UL grant is used for scheduling all the plurality of consecutiveUL transmissions, or wherein the at least UL grant includes a pluralityof UL grants, and each UL grant is used for scheduling a respective oneof the plurality of consecutive UL transmissions.
 27. A method for auser equipment (UE) to use in a 3rd generation partnership project newradio (3GPP NR)-based wireless communication system supportingoperations in an unlicensed band, the method comprising: receiving atleast one uplink (UL) grant for scheduling a plurality of consecutive ULtransmissions on the unlicensed band, wherein the at least one UL grantindicates a channel access type as one of at least: a first channelaccess type based on a back-off, and a second channel access type basedon a fixed sensing duration only, the fixed sensing duration including16 us and 25 us; based on the indicated channel access type, attemptinga first channel access to perform an UL transmission, which is not alast UL transmission, among the plurality of consecutive ULtransmissions on the unlicensed band; and based on (1) the first channelaccess corresponding to the second channel access type with a fixedsensing duration of 16 us, and (2) the first channel access beingfailed, attempting a second channel access to perform a next ULtransmission among the plurality of consecutive UL transmissions,according to the second channel access type with a fixed sensingduration of 25 us.
 28. The method of claim 27, wherein, based on (1) and(2) being satisfied, the second channel access is attempted according tothe second channel access type with the fixed sensing duration of 25 us,regardless of the indicated channel access type.
 29. The method of claim27, wherein the at least one UL grant is received via at least onephysical downlink control channel (PDCCH), and the plurality ofconsecutive UL transmissions includes a plurality of consecutivephysical uplink shared channel (PUSCH) transmissions.
 30. The method ofclaim 27, wherein the plurality of consecutive UL transmissions iswithin a channel occupancy time (COT) initiated based on a downlink (DL)transmission.
 31. The method of claim 27, wherein the UL grant furtherindicates a channel access priority associated with the indicatedchannel access type.
 32. The method of claim 27, wherein the at least ULgrant includes a single UL grant, and the single UL grant is used forscheduling all the plurality of consecutive UL transmissions, or whereinthe at least UL grant includes a plurality of UL grants, and each ULgrant is used for scheduling a respective one of the plurality ofconsecutive UL transmissions.
 33. A base station (BS) for use in a 3rdgeneration partnership project new radio (3GPP NR)-based wirelesscommunication system supporting operations in an unlicensed band, the BScomprising: a communication module; and a processor controlling thecommunication module, wherein the processor is configured to perform adownlink (DL) transmission without sensing a channel in the unlicensedband, when: (1) the DL transmission shares the maximum channel occupancytime initiated by a user equipment (UE), and (2) a gap between aprevious UL transmission and the DL transmission is not greater than afixed duration, wherein the fixed duration is 16 μs.
 34. The BS of claim33, wherein the processor is further configured to perform the DLtransmission by attempting a channel access based on the fixed durationin the unlicensed band, when the gap is equal to the fixed duration. 35.A method for operating a base station wirelessly communicating with a UEin the unlicensed band, the method comprising: performing a downlink(DL) transmission without sensing a channel in the unlicensed band,when: (1) the DL transmission shares the maximum channel occupancy timeinitiated by a user equipment (UE), and (2) a gap between a previous ULtransmission and the DL transmission is not greater than a fixedduration, wherein the fixed duration is 16 μs.
 36. The method of claim35, further comprising: performing the DL transmission by attempting achannel access based on the fixed duration in the unlicensed band, whenthe gap is equal to the fixed duration.